Aiming in paintball is alot different than when I was in the military. For starters, and this is for me, I think there is difficulty with sighting, while wearing a paintball mask, and using a stock, on a 98. SO, I would suggest using a sight rail. A BT one will work just fine. However, no matter how well your aiming, your paintball will do as it wants and so null and void the whole process.
Now, if you get the raised rail, like the M4, a handle and aiming sight, you will be able to sight using a mask and stock. One problem; Hopper. The Hopper's position on the 98, any type, makes it nearly impossible to use the raised rail that is like the M4. Side note: The rail attaches at 5 points and will not come off easily. If you get a good one, it will be more durable than you. Mine is still going strong after a few years.
Hmm, going prone w/ a paintball marker is a pain in the.. well.. lots of places, for me it is my shoulder, holding up everything because the tank is in the way. I know a way around this, but it is ugly as sin, and is impractical. You can PM me for details, but trust me, there are better answers. Read on.
Ok, so rigging an air feed on a 98 w/ most stocks is a really bad way to go(trust me). There is a BT Adjustable stock that folds. This does not, however, solve your prone question. So, after all that, I would suggest a Longbow Stock. The air feed connects at the rear and is ready for your remote. If you are used to Military shooting, the remote should not get in your way. However, it can be impractical in some paintball situations: see speedball. In Rec ball, I do not think the remote should be a problem. As for Prone, the remote feeds eliminates the tank, and drops, and so on.
LongBow Stock + Shroud + Bi-pod = good for your needs - the ability to use sights since these are paintballs. The longbow system fot the Tac-One (AirGunDesigns) allows for a cleaner profile. Yet, barrel length becomes an issue. For the 98C, or any Tippmann, a Stock may help with your personal preference. Please feel free to PM me with any questions. I have had my 98 and 98C for many years.