1” weld at most, then skip 12”, 1” more weld, skip 12”.... go back after first weld cooled and add 1” weld ... keep going till all welded up.
But first, run some test beads.
There are some good (and cheap) Chinese inverter welders on the market. I bought an ahp alphatig 201 for under $700 and I like it for what it is. They also make a mig, but it is being sold by eastwood and ahp won’t sell them direct. I don’t have personal experience with them, but some claim the harbor freight inverter welders are decent too. But their prices are near the other Chinese inverter welders. I’m not a huge fan of flux core mig, but that is really the cheapest way to get started. The gas shielded mig costs more due to the bottle, regulator, and gas, but I think produces a cleaner weld.
If interested in learning, surf weldingweb.com They will point you in the right direction on how to get started.
Also, most community colleges have leisure learning welding classes. I took one with my wife almost 20 years ago and enjoyed it. They did a good job teaching the basic fundamentals. After that class you would be more than able to weld in new floors.