any indication of size should be on a decal on frame... assuming this bike had a threaded setup, you cant really do too too much about your reach, you can move your seat forward but that will be your limit unless you start spending money on components... if the bike doesnt fit well, you may want to consider putting it on craigslist and searching for something that fits you better... not just comfort, safety. When you stand over the bike frame, how much space is between your delicates and the tube? can you stand flat footed?
my LBS loves the Nimbus tires, one of the girls that works there has a self claimed tire problem and said the nimbus holds up very well against her. check with your local shop, they are a pretty commonly used tire. not sure what the price tag is but $30 should be plenty adequate (per tire)
i use the michelin city's on my bike, nashbar has em for like 25/each
http://www.nashbar.com/bikes/Product...5_10000_201490
they also have other cheaper options.
(btw, they werent nearly as hard to mount as the reviews say...)