First thought is sb has equity while bluffing when called preflop. its not a river decision where a bluff has zero equity. So i think that means you dont have to defend 30% necessarily. But i would defend more playable postflop hands if they have a 10% 3b.

Corgi already said about equity. If we never play postflop we need to defend ~1/3 combos, but because we will call some hands vs 3bet we have to fold much less.

However you got good point, ''nitty range'' probably more profitable at micros considering rake and overfolding not a huge issue. Woudn't want to expand this range too much, but certainly can due if my opposition play not good and let me win more postflop or realize too much equity.

If we know villain tends to fold a lot to 4B, what ratio of value to
bluffs would use ? 1-2, 1-3 ?

This would depend on how many % he is folding. He can fold 60% 70% 90%, vs all those numbers in theory* we can 4bet any 2 cards. In practise it is easy to notice and hard to get database to confirm high folding vs 4bet numbers

Gl!

Your thought process has at least two errors:

1. If you defend by calling he can still win the hand. This was already pointed out.
2. The BigBlind is in a way helping you to prevent SB from making autoprofit.

I would defend any suited Ace and pockets down to 55 and more suited connectors like T9s, 98s, 87s, 76s