I've always been a fan of the DWS 06+. Very smooth and quiet. Great tire. The Michelin Pilot Sport All Season may be a tad better as far as handling, but both are solid choices.
Going to the 20" wheel will give you a lower profile, wider tire that will improve handling right out of the gate. You can address ride quality with the tire that you choose, but you will still notice a stiffer, performance type ride. Appearance will definitely an upgrade. Best of both worlds...
Take a peek at Voxx wheels. They have a great looking, wider wheel selection!
https://www.discounttiredirect.com/buy-wheels/wheel-replicas-gt50/p/66112?exactmatch=true
Most tire manufacturers have a 6 year warranty on their tires. A good rule of thumb would be to replace them after 6 years. If they are in good condition, maybe longer, but after 10 years, replace them for sure.
Not a lot of options in an A/S run flat. Take a peek at the Continental Pro Contact GX.
https://www.discounttire.com/buy-tires/continental-procontact-gx/p/34484
Hope that points you in the right direction.