Congratulations on your new purchase!
A couple of answers to your questions
1. People are continually parting out boats and selling rudder blades. Keep an eye on the for sale section in this forum
2. You need to be more clear on where the movement on your corner pylons and corner castings are coming from. If the pylon is moving inside the hull, that is a real problem. It means the shoe, in which the pylon is attached to the hull, is loose and will need to be reglassed to the hull. On the other hand, if the corner casting is loose on the pylon, that is an much differerent and easier to resolve problem.
a) The first things to look at are how tight your tramp is. It should be VERY VERY tight. Rule of thumb, the side bars should be bowed in about 1 to 1.5 inches. Tightening the tramp can definitely help tighten the boat.
b) Check the rivets in the corner castings to the cross bars. Sometimes, they get loose over time. If they are, replace them.
c) Finally...Over time the hole in the pylon enlarges and the bolt no longer keeps the casting tight on the pylon. That leads to movement, which slows the boat down as you sail through waves/chop. As these holes become elongated and not just uniformly larger, the only method is to epoxy the frame together. Its not as big of an issue as you might think. A summary of steps can be found at this link
http://www.thebeachcats.com/index.php?name=News&file=article&sid=82&theme=Printer. The end result is a
very tight boat
3) INSPECTION PORTS. Rule number 1. Don't cut into your boat. Rule number 2. Don't cut into your boat. Rule number 3. Don't cut into your boat. Of course...there are exceptions. If your hulls are still solid (when you rap your knuckles on the top of the hull in front of the pylons or anywhere else, the noise you hear is sharp and clear and it feels hard vs. soft and mushy), you don't need to do anything. People usually cut into the top of the hull as part of repair job.
4) Finally...you can add another trap wire very easily by ordering it from your Hobie dealer. I have seen double traps from one wire, and adaptors that fit on the mast to make singles doubles, but the quickest way is to just order another set. Putting them on is a cinch. One suggestion however. If you don't know how old the rigging on the boat is...just invest in all new rigging. The peace of mind on a choppy gusty day, to know that your mast will stay up...is priceless.
Have a great time with your new boat. Now you just have to wait out the Spring thaw to get it on the water!!