Brake Install North Ma or Southern NH

There is something going on with my brakes. I seem to be loosing fluid. I have yet to determine from where but the system is old and thought I could upgrade. I was thinking of a couple scenarios. Right now there is a 4 lug set up on the car and SSB makes a kit that will upgrade the rear to disc. New master cylinder and rear calipers, disk etc and parking brake. The other would be to completely change the system to 5 lug with a complete system (possibly a cobra from FMS). This is what I want to do but I don't believe that it would be the right thing to do right now. Not only would I have to change the entire system but I would have to get new rims and tires and throw away my summer and winter set that I currently have.