What are the advantages of using a tapered main sheet? Ive got what I assume is stock line on my Viper. Do I need to be able to splice line and make it myself?

The advantage is less friction, hence you don't need to pull so hard any more to get the leach tight.
You can buy tapered lines if you don't want to splice. Or you can make it by removing the core or by removing the outer braid or by splicing a thiner line into the thicker one, depending on the sheet construction.
Easiest and maybe most elegenat way is to have a rope with strong braid and soft core, where you can remove the core and still have the strength, eg.g Liros "Magic sheet"

Alternatively, you can buy something like 2mm or 3mm dyneema and some length of 6 mm (hollow) swiftcord (open weave) and simply run the thinner line through the swiftcord. Stitch both lines together near the blocks and then massage the swiftcord tightly around this core and stitch the other end. Thus you'll end up with a thicker line in your hand as the hollow swiftcord now has a core thus resulting in a 8-10 mm thick sheet and it has a 2mm/3mm tail that runs throught the blocks. A large part of the friction through the blocks is associated with the thickness of the line and not so much with its weave. So you don't really have to strip the protecting outer braid from the dyneema line. This makes it alot less sensitive to UV degradating etc.