Anyway I was wondering if any Battlespire Veterans would mind sharing any advice on what advantages/disadvantages to take

So far I've been taking

Disadvantages:
Forbidden Weapons: All except Longblades
Critical Weakness: Poison (apparently there's only one enemy who can poison you)
All starting skills reduced to 5%

Advantages:
Regenerate Spell Points
Increased Magery 3x INT

From my limited play experience (farthest I've got is the end of level 1 (bug prevented passage to level 2)), regenerate health is unnecessary if you have regenerate spell points and restore health spell. Is that true for later levels?

Any other disadvantages will low drawbacks?

Are there any other advantages worth taking? Athleticism? Adrenaline Rush?

Most of your time will be spent running around magic casters to make them waste their spells or hit each other before engaging them on melee. Because of this, you should take absorb magic. Regenerate spell points and 3x int mana is also a must have.

For other players reading this, I will point out that Spell Absorption is a very costly advantage (2500 points)

Cheaper alternatives include the Spell Absorption Spell (880 points) and the Spell Reflection Spell (960 points)

It should be mentioned that the spells don't have long durations.

The initial spell point costs for those spells are pretty high too. Raise your Mysticism (absorption) or Thaumaturgy (reflection) high enough, and the spell cost will be negligible (spell reflection goes down to 9 points/cast with 100 thaumaturgy, I don't use the spell absorption spell so I can't comment about the lowest cost there)

I agree, get spell reflection instead of spell absorbtion advantage. With this spell you can even take critical weakness to all elements which will give you loads of points to spend on other important skills. For your first playthrough, take long blade, thaumaturgy and restauration as primary skills and don't forget to get the healing spell. Strength and intelligence are your main attributes, wisdom is kind of unimportant when you're playing a breton.

Yes it costs much but it also has it's advantages and it's a different way to play the game.