Battery relocation is good for weight redistribution, but definitely not weight reduction. The extra heavy gauge cable run to the back of the car is always added weight, and I believe that battery boxes should always be vented to outside, even if you are using an Optima sealed battery.
One "trick" that I've seen that I really like for the ground connection, since copper is a much nicer conductor, is to use 1/2" copper plumbing pipe to run an alternate ground underneath the car along the frame rail. It's lighter and cheaper than 4AWG stranded cable, and still a very capable conductor. I've also seen people use this running a ground to a high power amp rack. The car chassis should really be adequate until you get to fairly high power, of course, but I generally like my starter and alternator to have a nice connection to the battery negative post. Since 10' of 1/2" copper pipe is like $10 at Home Depot, and it won't sag underneath the car, it makes it dirt simple to run along the frame fails.
When it comes to DIY, I tend to dive headfirst into about everything. Body work is one of the things that probably has little impact on the safety and driveability of a car. It does of course have a lot to do with the appearance, so I probably wouldn't have started with a "nice" car. That wasn't the case when I started, and I turned an old rust bucket into something that at least LOOKED like a nice car. Well, I suppose that it went through stages from "rust bucket POS" to "Some amateur's project car" to "Should have got Maaco" to "look at the runs in that paint" to "Hey, that's in pretty nice shape!" Now I'm reasonably confident that I have the skill, but I haven't done metallic or pearl paints before, and that's what I'd like to do on the Supra.