Re: Begining training in Aikido
I'd say just start with a general program to develop aerobic fitness. If you're not currently engaged in a regular program of aerobic exercise at a level that produces a training effect, then just work on basic aerobic fitness. Don't do sprints or intervals until you've developed basic aerobic fitness, which could be in a fairly short time (4-6 weeks) if you're not far from it now, or could take longer. I'd skip weightlifting for now, not because I think it's a bad idea, but because I think it's not necessary at this point, and it's a bit tricky to do in ways that will be helpful and not counterproductive.
I would also not try to teach myself ukemi, even with the aid of the very best video of the very best teacher out there. Ukemi is an aikido skill, and I don't think there's any need to try to learn the skills of aikido before you start training in aikido. What would be the goal of doing that -- to avoid stepping on the mat as a newbie? The desire is understandable, but I think it's better to learn aikido skills from your teacher and do them the way your teacher wants them done.