It will fit both of them.
Yes, the tippmann 98 and the tippmann custom are the same marker, therefore the threading of the barrel will be the same.
The 68 does not have a removable barrel.
The tippmann 98 egrip.
No, it is slightly different shaped.
No, it will not fit.
no, they are made by 2 different companies
CO2 or HPA will work fine with it
the one it comes with is good but most tippmann barrels should work
No, but any drop forwards with the standard two hole fitting will work.
Tippmann is a brand, not a gun. In general Tippmann's are viewed as the most reliable and durable guns on the market. This is because they use very simple, hard to break, low maintenance parts, which is why they are used by most places as rental guns (usually the Tippmann 98). However this durability comes with many prices. They generally shoot slower, less accurately, and less consistently then guns of a comparable price (without upgrades). In short, almost every Tippmann product will work for longer then a comparative product, but not as well. Tippmann also has some of the best Military simulation kits available for its markers.
yes