You are starting out right by doing your research. It is a very rewarding hobby if you don't rush. Patience and research are essential.
Protein skimmer, I'd say yes if you can. It helps keep the water quality good. There are hang on skimmers and hang on the back filters. If you have a hex that is all equal sides hang on equipment can be hard to do because the sides are so short. Theoretically you can do fine with just a bunch of live rock and a protein skimmer. The rock provides a huge surface area for bacteria which will provide the majority of your biological filtration. A canister filter works (I used one for probably 15 years) but it does need a lot of maintenance, I'd stick with your hang on filter.
Power heads are a must but don't have to be expensive. I have several I got on amazon for about $12 each. You can go really expensive with these as well.
In my opinion live rock is essential. As I said above it is a major part of the filtration system.
I used to have a 40 something gallon hex tank. Originally I had discus in it but I upgraded to salt many years ago. I had a bunch of live rock, a snowflake moray eel, a blue damsel and a clarki clown fish. There are a lot of small fish that will do well in that type of tank. Clown fish, gobies, firefish, basslets, dotty backs, etc. You can't really do a lot of fish that are active swimmers (like angels, or tangs) because there just isn't the space for that but there are lots of other options. Personally I like the fish that swim around in the rocks.