As said above go with a Crossfire HPA Tank. I would recommend a 68/4500 optimal. Make sure its HP(high pressure)800+ PSI output.
As far as drops, I think the Psycho Ballistics Bullet drop looks the best. Your going to have to get an A-5 adapter to use a drop.(Lapco-DOP-Etc)
Go with the E-Grip all the way!!!!
Secondary Regulation: I run secondary reg. on my A-5. I get consistant shots as much as +/- 5FPS average. This is with HPA and a Palmers Stabilizer. The Palmers looks and works great on the marker. But they are expensive. $85, most regs are. But if your running HPA everytime, Again, as said above its not that nessesary.
Black Macrline Kit. 1 Straight ----- 1 90* fittings and a Macroline.
You can get everything listed at www.hotshotpaintball.com
where I got all my A-5 stuff, best prices and best shipping prices.