Start with HIIT, 7 minute workout requiring only a stool and a wall; initially you'll be able to do maybe 10 reps for each part in 30 seconds but slowly increas

Start with HIIT, 7 minute workout requiring only a stool and a wall; initially you'll be able to do maybe 10 reps for each part in 30 seconds but slowly increase intensity until you are able to hit 60-80 reps/30 seconds, then chain 1-2 more sessions in a row to make it all up to 30 minutes. That should give you a massive boost and initial trained state (in maybe 6 months). Then you can switch to a similar HIIT program with dumbbells. The key here is peak intensity for a very short time doing wonders but it's tough and you'll hate every single moment doing it while absolutely loving aftereffects.