From my point of view if you did acid before, you should be fine experience wise.
Thing about psilocybin is that it is safe, you can not overdose. Even if you would be taking some insane amount like 10-20grams dried. If you don't have any medical issues, there is nothing to worry about. (To have 50% chance of death(LD50) 80kg person would need to eat 1,12kg of dried P. azurescens (the strongest mushroom) or 11,2kg of fresh ones) Even intentional poisoning of oneself is very unlikely, I consider it not possible.
I would take 2grams dried if I were you. Then I would move to 5grams next session.
For people that never took psychedelics I would advise starting from 1gram probably.
If you want to get "deep" than 5 grams is the way. From some weird place of perspective there is no point of doing 2grams first. But also doing 5 right away is irresponsible and irresponsible things should be avoided.
I have never seen anyone taking their weight into account when taking mushrooms. My understanding would be that efficacy of the dose should be tied to the size of the brain... not the blood supply of your body. Humans having similar size heads and brains, dose is stable. If you would be other mammal like whale, your dose should be higher...
If by doing psylocibin fresh you meant "fresh mushrooms" then you just multiply weight by 10. 20 grams of fresh mushrooms would be 2 grams dried.
