As a previous poster suggested - do you know how big the frame is? Assuming you're in the USA and using imperial measurements for height, a 5'10" person will ride between a 54-56cm bike. For every 3" of difference, go up or down 2cm. I have three bikes that are 54cm, 55cm, and M/L, and they all fit a little differently for different purposes. Without knowing your height or the bike's size (a pic would help), we wouldn't really be able to give an opinion.
As for maintenance, you should ask what the $450 covers. If the bike actually does fit, and $450 gets it working perfectly, then maybe - but chances are that's not the case. If the bike's been sitting neglected for most of a decade, you're looking at least at new cables, housing, and brake pads. There's no guarantee if the wheel, bottom bracket, or headset bearings are any good, and repacking those could cost a fistful of dollars. Truing and tensioning the wheels, along with fresh tires, would be a few dollars more. This isn't taking into account new parts that may have to be sourced, too. Just for reference, I didn't have time to redo my own brakes one year before a Gran Fondo, so I sent it to a shop for pads, cables, housing, and new bar tape. Just that ran me $150.
If you're not yet comfortable riding at 24mph, I wouldn't worry about racing yet. I cruise at ~18mph and hit 23-24mph on long shallow descents, and I'm far too fat and slow to race anybody!
As for clipless pedals, I find them very useful in expanding the range at which I can apply pressure to the pedal - down past the 6pm position, to about 7pm. With flat pedals, you lose torque pretty much right at the bottom. Additionally, they help keep your feet on the pedals when your cadence starts getting past 80-90rpm.
My recommendation would be to take the bike to the shop, let them a) size you up, see if it's in the right ballpark, and b) tell you exactly what it is they'll be doing - they'll be able to tell you pretty quickly if it's just basic tuneup, or if the pads, tires, cables need replacing, or if you're looking at new bearings/shifters/other parts. I'd probably hold the line at closer to $200. Any more, and you might as well see what else is out there.