Any gun is special if it's special to you. I personally love 870s and it would be impossible to guess how many rounds I've fired through mine. My most recent shotgun purchase was another 870, a 12ga. "police" model to use as a platform for everything. I have 3 barrels for it, the rifle-sighted smooth-bore one that came with the gun, a 28" VR/Remchoke for clays/grouse, and a 21" VR/Remchoke turkey barrel. For everything I have into this gun, I could have bought something higher-end I guess, but the 870 got the nod. I'm very fond of them. To your question....
It sounds like you have an Express, and they're solid performers for the money. Period. First thing to do is clean (I include taking the choke tube out and cleaning separately, and cleaning the internal threads in the barrel) the gun, and familiarize yourself with the disassembly. Lots on YouTube. Not complicated at all. Keep the gun clean, and all metal surfaces with a thin film of oil. Express finishes will corrode if left wet, so if the gun takes a bath in the rain...or you suspect the internals are wet...total tear-down, wipe-off/out, air dry, re-lube, re-assemble. It will last forever with this small amount of TLC. An 870 tear-down takes me about 2 minutes if I'm REALLY taking my time, and that's only if I drop the trigger group out.
As for the slugs/deer~lots said already about that. Good advice.
Spare parts~if it's an Express, you may decide to upgrade the extractor if you anticipate the gun will see allot of hard use. I've never had an Express extractor fail, but an upgrade to a good one (non-MIM) would be an inexpensive thing to do. I wouldn't consider it a priority...but a good idea when funds allow. Other than that, I'd say get one of those $8 plastic clay throwers, some Winchester white box #7-1/2 shells, find a good place to shoot and find someone willing to lob clays for you. Practice practice practice on moving targets...and it's tons of fun. If you find the spent shells jam in the chamber, hit YouTube again and search "polishing an 870 chamber"...lots of good/easy/cheap methods of doing it. If you find your gun needs this, I'd be happy to send you what you need.
Good luck, have fun, and enjoy your new 870. You're a lucky man to have a wife who'll buy you a gun!