i am by no means shrek'd--i'm running more of a donkey situation here--but i almost want to say the critically overlooked piece is just having the space to do move about/stretch/calisthenics, that is relatively comfortable in all seasons and weather and requires little to no effort to put into workout mode or maintain. i have done 130 sun salutations at dawn over the last 26 days and it's because my mat is already rolled out and doesn't need to be fiddled with between the time i get out of bed and start into my set.

but ymmv. a lot of what has historically stood between me and doing things is having any barriers or excuses not to put a moments inspiration into practice.

Calisthenics are great. Resistance bands are also awesome, they enable many exercises, are cheap and take up practically no space.

I like kettlebells a lot but the do require you have a decent sized room with a tall ceiling, also there's always the risk of losing your grip and putting a hole in a wall, or sending it flying out a window and into an old lady's face. But if you get a light one the risk of that is pretty low.

I still do p90x videos from time to time. Pretty much just need bands and a pull up bar. You should be able to find it on most torrent sites still, I think.

Eat a lot of food with adequate protein, get a pull bar, and do calisthenics. While I'm not very large (because I struggle to eat enough food), I am pretty shredded and have a six pack with a well defined chest and v-taper, just from calisthenics. It wasn't even my intention, I was just doing it to help with back pain and get to a healthy weight (was very underweight before). The only equipment I use is a doorframe pull up bar. Correct form, controlled reps and doing hard enough exercises are key.

As for movements, to hit all the major muscle groups, you want to do a vertical pulling movement (a pull up), a vertical pushing movement (a pike or handstand push up/any overhead pressing movement), a horizontal pull (rows), a horizontal push (push ups), a quad dominant leg movement (squats/single leg squats/step ups)and a hamstring dominant leg movement (single leg rdls/Nordic curls). Calf raises and tibialis raises can be added to fill out the lower legs and injury proof the ankles. Hit these exercises often enough, close to failure at the end of each set, and the muscles will grow. There are plenty of easier and harder variations of all the above exercises. I started out by doing push ups against a wall, and attaching a rope to my pull up bar so I could use my legs to assist..

I'll echo the calisthenics, resistance bands, and kettlebells in that order from cheapest to more expensive. Heavier double kettlebell workouts will make you yoked out.

If you have more space and more money, a barbell and bumper plates for doing some deadlifting, pressing (overhead and floor press variants included), rows, cleans, jerks, and snatches. These aren't strictly necessary (but are fun) because kettlebells will make you strong enough for anything life can throw at you and give you great strength endurance to do any sort of manual labor you'd need to do in life.