When following a stb extraction on 500g of mimosa hostalis root bark when you do Naptha pulls how much naptha would you advise using per pull and how many pulls.

Also when you use activated carbon to remove the coloured impurities are recrystallisations still necessary?

I wouldn't do a 500g extraction, that's huge. Scale it down to 50g or 100g.

For STB you are following 1.5:1:1 formula.

1.5ml water to 1g MHRB
1ml Naphtha wo 1g MHRB

so if you are using 100g MHRB you need 1.5l water (3 X 500ml) and 300ml naptha (3 X 100ml for each pull)

example Noman's Tek

Activated carbon is unnecessary and will just decrease yield. What you really need after a STB is an a/b or recrystallization to get all the lye and plant crap out of your spice.