That's great. Congratulations, Merry Christmas, and Welcome.
Others here have deeper TR3 expertise, but here are just some thoughts:
a) buy the official Workshop Manual
b) stock up on some good tools, including feeler gauges, wrenches, and brake tools
c) replace the brakes with new if necessary, and bleed the system thoroughly with new wheel cylinders where needed
d) be certain your fuel lines are clean and clear, and that the tank is in good shape. A rusty, dirty tank or bad lines can fool you into thinking you have more serious problems which you actually don't have
e) keep it dry and in a garage if possible
f) address the main cosmetics so you'll always have pride of ownership
g) put good wheels and tires on the car
h) keep it stock, though conversion to rack and pinion steering, and a carb upgrade would be good. Maybe other little things
i) keep the floor free of rust, and use good insulation, sound "deadener" and carpet
j) be sure your generator is in good shape and look for hot wires to avoid problems
k) if the engine, compression and valves are in good shape, just keep the points and timing on target, and the fuel mixture right, and there shouldn't be any dependability issues
Good luck. And have fun.