A few comments:
Picking the right philosophy depends on both the players you have and your personal preference. Playing "fluid" requires (a) a tactics where players have roles that are not highly specific to their attributes (e.g., FB-WM, CM-AM, W-AF/F-Poacher) and, conversely, (b) players with attributes sufficient to show some flexibility. Also, I personally prefer to keep my players on a short leash and want them to stay in formation -- particularly when playing a larger team, where one mistake may well cost you the game. Consider Chelsea playing Bayern in the CL final: would you say any team played with a lot of positional freedom? I think not. So, I agree with Julian that going fluid as a basic setup for the Arsenal "big team" tactics may not be the best point to start. Go "balanced" or even "rigid".
Arsenal is made to play 4-5-1 or 4-2-3-1. The first formation works probably best with defensive/counterattack mentality and the second - with control/attacking. However, you can successfully employ 4-5-1 to control the field, provided you have the right players and play in the right-sized field (i.e., small). 4-5-1 is good when you are able to hold the ball and take control of the midfield. This means killer passes, MCs able to both defend, and run forward to join attacks or shoot from distance. Your wing players should be able to operate in the midfield, too, i.e. IFs, preferably with the "cuts inside" PM. Your lone striker needs poacher attributes. If your wingers are made to hug the line, you need a very good TM.
3. PLAYERS & ROLES
Generally, you should have one playmaker on the field - just like in an army, you can't have an army where everyone is a general. So you should select one guy only. You picked Song -- not the best choice, IMO (see Julian's post). With 4-5-1 a DLP is the most preferred type of playmaker. But Arsenal just doesn't have a player to do the job (unless you bought one). You have your lone striker set as CF, which is the right choice for your formation, but not necessarily for your players. Looking at the players one by one:
GK: You have ter Stegen as defending GK, even though he has very good distribution attributes, plays with both legs and is good at communication and command of his area. You may want him to work some more, particularly when building attacks from your defense. [By the way, what happened to Szczesny?]
CB: Koscielny and Otamendi, both playing default roles of CD -- I don't like it very much. Otamendi has good defensive attributes and performs well under pressure. But he is VERY short for a CB [I retrained him to play Anchor], and performs best when paired up with someone more proficient with his head, who would go forward acting as Stopper. Otamendi can then sweep balls as your last man [Cover]. And you have to be careful with instructions when defending set pieces. Also, both Koscielny and Otamendi, unlike Vermaelen, play only with their right foot. And, at least for quite some time, they may struggle to understand each other because of the language barrier.
FB: Gibbs and Sagna are two very different players, and yet they have the same instructions in your team. Gibbs is poor with his basic defense attributes, at least until he develops, plus he desperately lacks match experience [he has potential though, and, importantly, he is Home Grown/Trained in Team: which gives you one extra slot when registering players for the league and the CL; the same goes for Szczes, by the way]. If you play Gibbs, make sure you ask him to do what he is capable of doing: run. Not much creative freedom, no tight marking, no diving into tackles, no long shots, no through balls. Keep it simple: he should run forward and pass the ball to a winger or try a cross, and then loosely cover his man by staying on his feet and blocking crosses/passes. This way, he has a chance to make up for his poor tackling and positioning.
Sagna is experienced and a working horse. He should run a lot, and he is very good defensively, although not great at crossing and long shots. Plus, I found him very useful for attacking/defending corners.
DM: Song - DM or Anchor. Not a DLP material. But, again, he is not very tall, nor super fast. If you use him as support and ask him to run forward, he may fall behind his man when returning, if the opposition plays someone like Mata in the AM position.
CM: Hazard in the middle - not a good position for him, IMO. He is close to useless defensively, terrible tackling, marking, positioning, no bravery and aggression, too low determination, teamwork and work rate. No good with his head, either. And he is barely 172. His anticipation, decisions and composure are also below top class. He should play as winger. Ramsey as CM - it makes sense. But Ramsey has little experience, is not very strong or aggressive, very poor with his head, and needs time to improve his tactical atributes, too. He may be OK as right CM when supported by Song and Sagna, provided those two players' focus stays on the defense.
W: Gervinho as supporting LW - in theory, it could work. He is very fast, great off the ball, flair, technique and dribbling, made to run with the ball and beat the opposition. He also has good key striker attributes: finishing and composure. Therefore, he is best employed in positions where he can focus on attacking, roaming into the opposition's box, going past defenders and becoming a poacher chasing the ball played into space [I put him on positional training as a forward]. He is not a great passer, though. And, being right-footed, running along the left line and crossing is not the best thing for him. Also, look at your left flank: you have Gibbs (attacking fullback), Hazard (attacking winger playing as LCM), and Gervinho. None of them is good at winning the ball or putting the pressure on the other team. This is asking for trouble.
Wilshere as supporting RW - it is not true Wilshere can only play as CM/AP. He *can* be very efficient as winger, provided he plays IF (preferably right). He is not an explosive winger-become-poacher like Gervinho, but he is strong mentally, a great passer, able to stay on the ball and do something creative with it. He is also pretty good defensively for a winger, which can be useful when playing against a strong team with attacking fullbacks.
CF: RVP as CF - I know many people play him in that role. I see him as trequartista, playing behind Chamakh or another powerful forward. RVP will not put any pressure on defenders, and he is not quick enough to be a real poacher. He lacks raw physicality and heading to be a true TM (although he is pretty high, and has lots of bravery and aggression). So should he be a CF? I personally don't think so. One other reason is that he is prone to injuries, and leaving him to fight for the ball with Premiership-level defenders is the best way for him to end up injured for 3-6 months. One such injury and he will likely never return to his current level. And if you choose RVP to play as your lone striker, you should make sure he gets enough support from the midfield and wingers, with short, quick balls played to his feet. With 4-5-1, and him being the only attacking player (except for a CM/AP), it just ain't happening. He won't get enough balls. He won't have enough good opportunities to pass to someone else to finish. With a setup like that, play Walcott or Gervinho instead - especially when you're counterattacking. Or use Chamakh, he is pretty good (better than IRL) as TM/DLF-Attack, particularly when you play more direct balls to head he's the best man for the job you have.