Good to hear. Since you're clear to train and the only limit is your current conditioning, then treat yourself like a "beginner" and just get back into a routine with gradual progression. No worries.
If you're working the bags, I usually have people start with a 1:2 ratio, like 30 seconds work with 1 minute rest, then bump it to 1:1 (60 seconds each) after a few weeks.
That walking routine is also solid. Whatever specific cardio workout you do, it's fine to go low intensity as long as you're consistent. High intensity stuff is great, but don't feel like it's necessary.