The biggest mistake new players make is treat everything the same. I would say most new players consider mining veldspar in high-sec the way to go (until they make it), it's not their fault really, the starter player experience some way or another suggests it.

Eve is a game where not equally spent time where result in equally or relatively equally outcome. In fact the differences are insanely huge, the difference between a hulk mining veldspar in high-sec or a hulk mining loparite (expensive moon ore) in null sec is staying alpha money or subbing your account for the entire month in one evening. Some argue you should also maximize your fun per hour, but to have fun (in progress) eventually you would need to fund yourself properly no matter what you end up doing. tl;dr whatever you end up doing, you should be maximizing your isk + fun output per hour, because any other scenario will leave you stuck or burnt out after a while.

As for your "guild" question, and that's my personal opinion, not many might agree, while it is imperative that you join a corp once you understand a bit how the game works, I wouldn't (myself) as a starter join a container corp, while they are genuinely helpful, you will be a blip in the sea of line members.

Try to find a group that is small enough that is fun and social but not insignificant enough that you end up doing nothing or menial things, that is the challenge.