That should be a nice bike... good find.
I've had great results with dish detergent and water to clean the frame. I use old tooth brushes in the tight areas. Rinse it with clean water (I like a spray bottle) and wipe with a soft cloth. Follow that with an automotive cleaning wax like Meguiars Cleaner Wax. It will protect from rust for a while.

Most things that really remove rust will damage your paint and/or decals too, and I've not found a good solution other than a bit of WD-40 or 3-in-one type oil to loosen the rust before washing and waxing it.

I've used Zep Big Orange aerosol ($12-15 in car parts stores) to clean bare alloy parts like derailleurs, metal brake parts, cranks, etc. It REALLY works with hard to reach old, hard gunk and leaves the alloy parts sparkling. Be sure to rinse it off immediately and dry the parts with compressed air if possible, then lube where appropriate. Tried many others before Big Orange and it is in a class of its own for aluminum alloy parts.