Roll outs: Roll outs are a major nuisance especially when you first start out, but there are several products that prevent them.
1. Detent Rings made by CCI. These are the cheapest option, but also the least convenient. To use them you match the size of your paint to a ring then put that ring into the breech before you screw your barrel on. Matching paint can be a bit tricky, and if the ring is to large it does nothing, if its to small it will cause your paint to break. The other down side is they are very easy to lose, once you unscrew your barrel nothing holds the ring in place and it can fall out(I do this all the time).
2. After market detents. While CCI doesn't offer anything like this there are places to send your phantom to have detents that perform like any normal gun installed. The two I know of are Air soldier paintball and Super Stanchy customs. I don't have personal experience with either, or know if they still do it.
3. Freak Barrels. If your not familiar with the freak system, its a barrel that can take metal inserts of various sizes. This allows you to always match your barrel to the paint you are shooting. When this system is used on a phantom you can tightly match your paint to the insert which will prevent roll outs and improve your guns performance slightly. This is the most expensive option, and again I have no experience with it. Freak inserts are available through GOG paintball and barrels are available through CCI. Other freak barrels are available, but CCI uses its own threading which is hard to find, plus the barrel diameter may not fit through the pump handle.
Paint feeding Set Up: How paint is fed is determined by the front half, or breech of the gun. For stock class there is only one breech option. The stock class breech is composed of three parts, the breech itself, the mounting block which screws into the breech with 1 screw, and the feed tube which screws directly into mounting block. Feed tubes are available in 10 and 15 rounds, I recommend 15 because as it allows you to have paint in your gun while reloading.
For open class, there are 3 different options.
The first comes in three variety center, left and right. These have a pipe on them and use aftermarket plastic elbows to hold your hopper
The second has a threaded port which allows clamping feed necks to be screwed in. This only comes in center feed. I'm not sure what threads they take.
The last option actually uses the stock class breech. You remove the mounting block and screw in a threaded adapter which can take CCI or aftermarket clamping feed necks. Again I don't know the threading and have heard these can break if used with a heavy hopper.
Air: The first thing to look at for is is your grip. CCI makes two types of grips. The first is a plastic M-16 style. These have no mounting options unless you buy a mounting block with it.
The second type is the 45 style frame. I really don't know that much about these so definitely double check the info I give you These have screw holes for mounting but I think the bottom of the grip has a strange angle making them only compatible with CCI ASAs.
The second thing to look at is how you attach the valve to the ASA. The two common options are to run a steel braided hose directly from the valve to the ASA. This is cheaper but the hose can be in the way a bit, and looks kinda ugly in my opinion.
The second option is to get the vertical air set up then run a line from the vertical ASA to the ASA on the grip. This keeps all your hoses out of the way and looks nicer, but will be more expensive. It also give you a place to put a regulator.