Complete floor replacement advice

Wheel ramps are preferable to jack stands. If using jack stands 2 under axle tubes and 2 under front frame rail as far forward as possible. I like to put them between the front and rear k-member mounting pad.

To remove your old floor most people use a spot welder bit to drill out the spot welds. I personally prefer to grind them down with an angle grinder. I don't believe you need to install the frame connectors first if you have it supported correctly. Make sure the doors open and close properly without dragging and jamming before you weld anything in solid you don't want to weld your car into a tweaked position. If you haven't purchased the frame connectors yet look into the ones made by uscartool. They are the best looking piece I have seen and their other product lines have good reviews.

While you have the floor out it would be a very good time to add some additional bracing and reweld the torsion bar crossmember socket. The original welds were barely adequate on many cars. I have seen cars that were only welded on roughly 1/4 the diameter of the socket on 2 sides.