winnerke 123, greetings!
You are where I was a while ago.
1. My best guess is that $50 [USD] is probably enough to start playing HUSNGs [regular speed] , but note I have not played on Stars, just the i-poker network.
2. I am not sufficiently qualified to answer about HU cash. The great difference is that, in cash, you can just walk away if you are feeling bad.
3. If you look, you will find many blogs here by successful HU cash players, and by HUSNG hyperturbo players. I am not aware of any blogs by expert regular speed or turbo HUSNG players - but I may have missed something.
4. If you google on the subject, yes, you will find websites out there which specialise in the HUSNG format.
5. I am not aware of any specialised HUSNG books - you will find several that are good on cash - I have often heard Will Tipton's name mentioned in this context.
Comment.
Please note that these are not the words of an expert. In my opinion, HUSNGSs are a field where Pokerstrategy.com is currently weak. There are no dedicated strategy articles. There are a number of videos, which you may find helpful, but there is no coherent, integrated educational model for PS members to follow. The site has a partnership with the specialised site husng.com, which provided us with some of those videos, but the partnership is intermittent, rather than being visibly active.
If you look on YouTube, you will find a lot of free educational material out there, which will be helpful - provided always that the rest of your life gives you the time to take advantage of it.
Never forget that the hyperturbo format is a different game from regular and turbo.
I have my own blog for regular speed HUSNGs, but I would not describe it as educational.