Research is definately what you need to do.
I would be concerned with the rust. What you see is only 10% of what is really going on. Tip of the iceberg as they say. Considering the repaint, I would bet there is bondo (body putty) in more than one spot. Bring a vinyl magnet to check out the likely rust areas (lower fenders, dog legs between door and rear wheel, rear wheel arches/lips, lower front valance by turn signal lamps, rear deck under hatch, etc). Looks like the hood emblem is missing (and holes bondo'd over) perhap due to a accident? The nose of the Z is longer than you think and you can't see it when you are driving (a really good thing) some people tend to smack it into things...:P
I suspect he had the evil square top/square mouth hitachi carbs on this before he moved to the hitachi SUs. I think the sqaure tops cut in to production late in 1973 and lived on thru the 260Z until FI came in on the 280Z.
Charging problem cold be bad regulalor (fiugre $35)...looks like a fairly new Alternator in the pics.
Interiors can be $$ to fix - no pics of that...
I would say $800 is a fair offer.