New to Longbow and need guidance on tabs. First off, ill exclusively going to be shooting 3d with it until I'm good enough to hunt with it. Second, I shoot split finger on my Olympic rig but notice three under is very popular. What are the disadvantages and advantages of both? What would you recommend?

i switched to 3 under recently and am doing very well but i shot my best score  split but it was a very lucky day i shoot more consistantly 3 under

The positive of 3 Under is that many folks are more accurate shooting that way as they can gap shoot.  The negatives are usually a louder bow and a shorter "point on" distance.  I have shot both and prefer split.

Can you shoot either on the same bow? Or does it have to be a specific bow for either technique?

You can shoot either.  It's best if your bow is tillered for 3 under, but that's minor. My hunting bow is tillered split and it shoots just fine.  It's not any louder either, never heard anyone complain about that before.

I switched to 3-under this year after 40yrs of shooting split-finger. All my bows(and thats a lot)are tillered for split, and I can't honestly say I notice any difference in noise level, especially with the longbows. I do, however, put most of the string weight on my index and middle fingers with the ring finger just kind of along for the ride. Maybe this doesn't put as much stress on the lower limb and throw the timing out of whack as much? What I like is that it puts my point-on right around 20yds.

My is louder with three under, point on is closer.

It depends on the bow. All of my bows are tillered split, no difference on any other than one which I won't shoot 3 under due to it is just too far off tiller wise with 3 under.