Welcome to C&V lanky_chris!

I believe Thrifty Bill's assessment is right on - I would add that if you are seriously interested in upgrading your A08 the place to start is the wheels. Alloy wheels will make the single largest improvement in weight, ride and braking that you can make.

Going from cottered to cotterless can be expensive because of the price of original French threaded components, but as Bill points out there are a few more choices today than in the past.

Personally I am content with cottered cranks - but if I had to upgrade (and was not a purist), I would probably go with a modern French-threaded Grand Cru bottom bracket from VO. This would allow you a wide range of crank set options, new or used. Note however that the crank is what determines the bb - not the other way around.

That being said, you need to understand your connection with the bike, and how much you are willing to spend, because an alloy wheel set and VO bb together will cost more than what the bike is worth. You may be better off just servicing it as Bill suggests, and saving your money for another bike down the line.

PS - You can buy a good KMC 5-speed chain on-line at Niagara very inexpensively. Be advised though that of your rear cogs are worn, the new chain could skip, so you would have to replace the freewheel as well. Both tasks require some bike specific tools which you should invest in anyway. - You will find much useful information at the Park Tool website and at Sheldon Browns website. There is good general information at the My Ten Speeds site also.