You say no rust, how about bondo or any other sign of previous body work? It looks like it has a new paint job. After finding suspect areas by tapping lightly with finger tips, use a fridge sheet magnet to confirm any possible bondo'd areas. Safety first brakes- brake hoses, etc get it running replace all hoses if they haven't been already- radiator, heater, fuel, expansion tank all fuel filters- carbs, engine bay, filter inside of electric pump by gas tank. window- get it fixed before it gets worse, go through the other and grease it up before it starts giving you trouble. window chrome- possibly the rubber is rotted and hard(windshield and back window) suspension- bushings and shocks, unless the bushings are noticeably bad, hold off until you have a solid daily driver. Then do the struts and bushings together. carbs- are they the stock carbs for the '73? Either way, if it runs well leave them alone. No reason to replace. door latch-- handle or latch? Handle you can get a new or used, classifieds, etc. Parts-- You would be surprised what the dealer still has in stock. MSA has nissan parts, but their prices are a little inflated, Courtesy Nissan in Texas can get you most parts. Ebay also like MSA, inflated pars prices. Research before buying from anywhere. Tach-- Mine does the same thing. Sometime I can pound on the dash and it will start working. I will replace with a used tach, if that doesn't work I will find a early 280z tach, supposed to work better with the electronic dizzy i have. But that is not what the problem with the tach, possibly an internal short.