Welcome! As mentioned, your M10 isn't the almighty powerhouse that is the M42...but you're still welcome here!

$1000 for an E30 with rebuilt suspension is a gift! Kudos to your aunt for driving such a cool car! Wanna find out your car's birthday? Put the last seven VIN digits into this page, it'll give you the build sheet and some other history:
http://www.bmwarchive.org/vin/bmw-vin-decoder.htmlThe M10 is a superb motor; yours is the best of the bunch primarily due to the electronic fuel injection. No CIS or mechanical Kuglefisher nightmares for you! It's not a fast car, especially if it's an automatic. They are incredibly durable, however. Given good care, your car can easily see 400K miles. I'd suggest good filters (Wix, Mann and Purolator are all excellent) a cheap 15w50 synthetic like Mobil1 or Syntec, changed <10K miles or so (unless you race, live in a dusty area, or DD through a lot of traffic). I tend to buy whatever synth is on sale. IMHO avoid K&N filters.
Recaro seats are excellent but the E30 version is very rare indeed. Alternatively, you could upgrade to the very comfortable BMW sport seats offered in the iS models. BMW took their time making an excellent Recaro copy, and they're a direct bolt-in. Be sure to grab the matching rear bench seat.
Replacing a fuel tank isn't that much of a nightmare, but you will want to read up a few tutorials before tackling it. That tank is shared among the 325e cars as well...the larger 325i tank can be made to fit but I'd avoid that project. IIRC that requires dropping the driveshaft, you may want to tackle new fuel lines, fuel filter and new connector piece as well.
Given the low mileage, expect that all the fluids and every bit of rubber will need replacing soon. Especially brake lines/fluid, coolant hoses/coolant and fuel line. Only use high pressure fuel line! 5/16" can substitute for the 8x13mm OEM line in a pinch, but you might need new hose clamps. Stainless brake hose is a nice upgrade, but might not be easy to find for the earlier cars. Also be sure the coolant is renewed, Zerex Z05 or BMW OEM. A new water pump & thermostat are a good idea as well.
Be aware that her car has some differences from all other E30. You won't have ABS. You will have rear drums, different half-shafts, different rear bearings, different front strut tubes. If you want a useful speed boost, look for a 4.10 small-case LSD diff.
Have you logged into R3vlimited yet? Premier E30 site on the web. Find some local fellas with E30s...you could use some advise, and (let's face it) we're a heck of a fellowship.