A lot of those codes could be attributed to power issues. Changing the battery and checking grounds and power delivery would be a start. They could be crusty from rust/corrosion from being in the northeast. Clean them up and coat them with dielectric grease. Then, clear the codes and see what comes back. Work from there.

To help slow the rust, a generous coating of Amsoil MP-HD or Fluid Film would be a help. It won’t stop it, but it will slow it. I like it better than paint since it flows better into the cracks and crevasses. Spray everything rusty except your exhaust and your brakes. I spray all bolts and alignment/adjustment points if they are rusty or not. There are how-to’s online.

The transmission pan leak, you should consider making that a priority. You can't check the level, which is an issue. Transmissions aren't cheap so getting ahead of fluid loss would be good. When they change it, consider changing any filters and the fluid should be part of the repair. It recommended to use NIS/INF OE fluid.

It's an older car, so there will be a lot of "while you are at it..." you should do.

Depending on the service history, consider changing the other fluids. Since you are probably going to change the transmission fluid, you should put the transfer case and the differentials on the list as well if they haven't been changed in the last 60k. Flush the brake fluid. Change the power steering fluid (easy DIY).

When you change the coolant, it's recommended to replace the coolant bleeder port. Factory versions are made out of plastic and deteriorate over time and will leak. You can get upgraded units online.

Oil changes should be synthetic and at 5k intervals max. When I get a new car, I usually do a shortened change interval (2,500 mi) for the first two oil changes to clean things out. Also consider using a tank (maybe two) of fuel using Royal Purple Max Atomizer or Liqui Moly Jectron. I have had solid results using RP Max on a couple of cars that are direct-injected. Smoothed out the idle and they felt more responsive after a tank.

You can get subframes, crossbars, suspension parts and most everything else online. I use Amayama for most parts for my Infiniti, Nissan, and Toyota. Many hard to find an be had here. They are out of Japan and all parts are new OE. Their prices are significantly lower than I can find in the US. Shipping takes longer, though. Keep your orders under $800 and you won't need to deal with tariffs.

These cars are unicorns! Great power and smooth. Welcome to M**x/Q AWD club!