installing sub panel in garage off of house main
The 225A welder would draw 50A @ 240V on it's maximum setting. The 17,000 BTU/hr heater is electrically equivalent to 5kW, so about 21A @ 240V. If you want to operate both simultaneously plus lights (not much power required for those, however), you need a 100A subfeed to your garage.. 60A will not cut it.

A 100A subfeed to the garage requires 3/3 AWG NMD if the garage is attached and the cable is protected and not in a wet location. If the garage is separate, then you're looking at running conduit, with 3 AWG RWU90 line and neutral conductors, (minimum 6 AWG neutral conductor if your locality lets you run a reduced neutral), and a 4 AWG ground.

The breaker would be 100A, unless you can find one that's larger than 70A but less than 100 A. You will likely want to upgrade your service to 200A (Imagine someone using the stove and electric clothes dryer while you weld in your heated garage…) In my jurisdiction, a load calculation would result in a 200A service being required.