for the sniper mods, unless you're going for a scenario-look then just buy a good barrel, high quality paintballs, maybe a stock a remote line and a remote coil. snipers in paintball generally use quiet markers and upgrades as to reduce the risk of being spotted. i tend to have the opposite but thats just me.
scopes aren't as useful as you might think, but if you can get very good accuracy at maybe 100 feet or so then maybe 2x or 3x magnification may not be bad. although scopes in paintball are more used in large scenario games to scout farther away from the player to get a tactical advantage and spot people before they are spotted. i use a red dot sight and it works for me. aiming farther away can be a bit of a pain though because the dot will get in the way of the target (though you generally compensate for distance my aiming higher than the target). unless you are going to do some serious longrange(for paintball range) sniping, then save your money and get a cheaper red dot sight.
remember: a scope is a sight, but a sight is NOT a scope! a sight usually has a red/green dot for target aquisition with only 1x magnification(or no magnification) and a scope will always have more than 1x magnification and usually has a crosshair of some sort sometimes with a dot in the middle but that depends on the kind of scope.
laser sights are banned from field use depending on the field because all lasers have the potential to blind people and people generally get pissed off at people who try to point it in peoples faces to distract people by making them move constantly and unwantedly to avoid getting literally blinded forever! so i would recommend forgetting about them completely. although if you want you can buy one to practice and get REALLY good at shooting from the hip... but i wouldnt do that myself.
for the sidearm, tippmann came out with a new pistol and should be cheaper than the tiberius pistol, but im not sure about that pricing comparison. this is not an accurate reccomendation for either pistol but with reading reviews and watching gun tests on youtube have led me to reccomend both pistols, but the tippmann TPX over the tiberius pistol. good experiences with the 98C and some experience(though not much) with the A-5 have made me think good thoughts about tippmann products in general and hopefully that reliability and performance has been handed down to the TPX. the tiberius pistol shares a 12gram CO2 cylinder and 8 paintballs in one magazine, unlike the TPX, which has a 12gram in a separate place on the front of the gun instead of in the mag itself. the tiberius pistol is quite expensive so the TPX is the better go for the budget 'baller.
if you are ever wondering what to buy for any gun, no matter what it is... then it will likely be at http://www.pbreview.com
i read reviews here before i buy almost anything.