rudder skins are thin!
I suggest that you get a new skin for the rudder, especially considering they're 0.4mm (.016"), and as mentioned the cost of the aluminium parts from Van's is really quite cheap. Freight will cost though as it's a large flat delicate part, so if you can order with other things it won't hurt so much.
As for tips for getting started - there are some relatively easy bits to do on the -9 empennage (the VS is probably the easiest part, followed by the HS, but leave the rudder and elevators till you know what you're doing), or you could order the vans practice kit & toolbox to get you started on the metalworking basics. Use the old corroded skin for practice also - may as well get something out of it.
Take the time to read through all of the manual - especially chapter 5 that covers building techniques etc.
RV-9, Empennage and Wings about done, Fuselage taking shape.