Getting started I’d say most importantly is to find a community of martial artists to be around. Usually this means joining a gym, which can also mean choosing one art. I will say don’t let choosing scare you off. Never be afraid to quit never be afraid to pivot. There is no replacement for a proper mentor, shifu, coach or what-have-you when you begin.
‘Foundations’ are drilled extensively no matter the route you take and you will be better off for every foundation you work on. That being said it is impossible to throw an 80kg partner 1000 times a day every day, so foundations include balance. To stay focused enough not to rush through your learning experience is a difficult task when you see how far you are from the upper bounds, but injuries and expectations will set you back much further than forcing what can only work optimally with fluidity.
Bodily recovery is extremely important when training intensely for extended periods of time. Stretching (Tissue work), sleeping, hydrating, and eating enough are all invaluable aspects to your training.
All in all, I'm a fan of grappling oriented arts like BJJ, Judo, catch-wrestling, etc. But what art to study depends, in part, on what your goals are. Self defense? Fitness? Mental discipline? Making a living fighting in the UFC? Something more "spiritual"? Those choices could affect what makes sense for you.
Anyway, just go find a dojo and show up. In any reputable dojo the first session is free, and like any trial it goes both ways. See if you like the teacher and the nature of the art.