DIY repair advice

I bought my first car for 1000 dollars and it needs some work of course. The main issue was a small leak that I am pretty sure I fixed. There are a few more issues I’d like to work on that I believe are just cosmetic but may have some contribution to the leak in not sure about. I would like to know if there is anything I can do to fix these issues myself without having to pay someone for help. The rubber seal around my exterior has dry rotted a bit and the guards on the doors have begun cracking and changing colors. My main concern is the roof on top of the trunk has rusted and started to flake off. I’d like to prevent that from spreading as much as possible and prevent it from getting worse. If anyone has any ideas on how to diy fix these issues please let me know. Thanks in advance!