Hey mate. In the section above Basketball on the main page you will see a link to New Member Intros where these usually go.
Re your question of where do you start you probably should experience a bit of everything you listed to see what floats your boat. Buying boxes provides the fun of pack opening and seeing if you pull some James Harden mojo, but you need to appreciate that you will rarely find a box where the cards you get equal the value you paid for the box. I tend to hope for 50% value in cards and the other 50% in fun.
You can also go in Breaks where you pay for a spot in a break and get a random team allocated, or a pick your team break where you can buy a team. Maybe visit cherrycollectables.com.au and in the menu select Breaks and you will see some options. Again the risk is you get bugger all for your money, but it’s not a bad way to gather cards that you can then sell to build up your PayPal balance or trade for Rockets cards. eBay is a good way to target specific types of cards, but be aware there are people bidding their own prices up, plus there is now GST charged for overseas.
You could start here by posting a thread in the Wanted section saying the types of cards you are interested in, and members will post some pics for you to see and provide pricing.
Good Luck and Welcome!