Wagz,
IMO, you will probably end up doing a LOT of welding during your project, so my advice is to learn first. Welding is not rocket science, more an art than anything else. With some practice and basic knowledge (plenty of good & fairly short books around) you will be welding like a pro in no time. Practice is the key. Once your confidence is there, you'll have no problems. By the time you pay someone else to do it......$$$$$.
The sub frame connectors are easy to do, and if your floors are in good shape....all the easier.
I had to replace my floors when I did my SFCs. PITA, but easily done. Check out my pics if you haven't already, and put the car on a rotisserie...welding much easier that way. I built up my rotisserie in a couple of hours with about 15 bucks worth of steel.
Good luck....
Tim