Other users have given you very detailed and useful advice. I have personal experience with your last question:
"4- how many characters did you manage to put in a single scene without your pc giving up?"
My system has a decent RTX 3060 12GB VRAM card. I wanted to see the maximum it could give me. I had posted this topic about my experience:
https://f95zone.to/threads/being-a-dik-fan-art.29960/post-14452199
As a summary--> If we are talking about a normal scene with a background of 5-6 models, it may render, but very slowly. If you put 8-10, there is a high probability that DAZ will crash. It depends a lot on how many other objects you use - background, furniture, clothes and whether they are of high quality. The lighting of the scene also has a huge impact (more light objects will slow down your system). Also, what quality of the model you use (Sub level - 1 --> OK, level-3 --> gpu hell).
If you load one of the ready-made light assets and just put the models from BDIK without clothes, you will have no problem and you will be able to render more. If you try to imitate something like the award for the coolest costume from ep.9.....things are completely different.
There are a few options to improve things:
1. You use this add-on: Camera Doctor Bundle. It was recommended to me by
Sharyan and it really helps. You don't actually render anything outside the camera with it. Where can you find all the assets for the models, links were given by
Night Hacker.
2. There are videos on the Internet about rendering parts of a complex scene using the so-called 'Canvases'. Search the net for more info about this option in DAZ. For me personally, it's a bit complicated for a beginner.
I guess there are other techniques that more experienced people can share. My personal advice is to start with 1 model. That way you can focus on the impact of your render and the lighting of the scene. If you look more closely at the topic and people's works (including perhaps the best artist
lockhear), the strongest renders are with 1 model or at most with Tremolo and one of the girls. That way you will get a work with maximum character and impact.