The rivets for the winch can be gotten from FS Inc.  Dee, Karen or Harry will be sure you get the right ones.   They are kind of specialized and you may not find locally. Do you already have the winch?  The rivets are pretty easy to drive with a ball pean hammer.
The halyards are also pretty easy. The only catch is it helps if you have the tool for squeezing on the metal stopper that keeps the halyard from coming off the spool if  it unwinds completely.  Do you have a fleet nearby?  Usually someone in most fleets will have one and know how to use it.
Most fleets would welcome you, as long as you have safety gear and cut some slack for you to get the boat legal.  If you go to a sanctioned event like the NAC, MidWinters or Wife Husband,you will need the boat legal.
Locally, most fleets will let you race as you figure out the boat, with the exception of the unlikely possibility that you would use some some illegal element to clean everyone's clock on the course.  At districts, and above, or serious regattas, the expectation is that you will show up with a class-legal boat.  That is what one-design is about.
A good guide is that if an event is big enough to have two fleets, championship and challenger, then it's likely big enough to need a class legal boat, and not too much slack. 

By the way, your local fleet can often help you get the boat legal and raceable.  It's is everyone's interest to keep the Scot a one-design.  It makes the racing more fun and keeps the value in the boats.  Most fleets have some folks who have centuries in the Scot combined.
On your rub rail question, is that an aesthetic choice, or is the old one messed up?  If you put a wood rail on the boat, you will increase the maintenance.  New aluminum from Harry probably costs less than really good straight-grained hardwood in over 20 foot lengths.  Bob Neff, the FSSA measurer, can answer definitively on the class legality of the wood rail.