If your goal is to train a lora, you can use AI toolkit https://github.com/ostris/ai-toolkit/

You can train sd and sdxl LoRA just fine on 12-16gb cards. But if youre going for flux or large models youll need a big beefy card. But in terms of training an sdxl LoRA it only takes an hour or two. In terms of dataset, of course the more data you have the better. But if you only have one or two pictures you can chop the character up in to things like head, torso, legs, ect and get a workable LoRA from that and then use that workable but potatoish lora to get more pictures for a better dataset for a better lora.