Transplant seedling to 3 gallon or 5 gallon fabric pot?

Depends how long you are planning to veg the plant. That will define how big the plant going to get and how large the root ball will be. There’s no reason you couldn’t germinate the seedling in its final pot really. Though some argue letting plants become a little root bound and transplanting can improve the density of the root ball. For the size of your tent you probably only want to veg for 7 or 8 weeks, a 3 gallon pot would do fine. I might transplant to 5 right before flipping the lights. You will have an opportunity to reassess and repot the plant into a 5 gallon at the end of the veg cycle when you flip it. This strain is mostly Indica so you probably won’t get a tonne if stretching in the transition to flower... I’d try to keep an even canopy and flip when ~ 60-70% of the surface area of the tent if filled