Hi @360George !
It’s hard to recommend “the best gsd values”. In my professional work we aim for 1 pixel = 1mm due to it being survey work for heritage sites in the UK.
Depending on how much detail you require will determine what GSD to aim for. Do some tests at various distances and see what you like - you can use a GSD calculator to see what distances will give you what spec.
The most important thing to remember for photogrammetry is “garbage in, garbage out”; i.e. poor images will lead to poor results, so make sure you know how to expose your images correctly first.
If there’s anything else you want to know just ask! 
Also there are loads of resources here on the forums under learning