You can't drain in-ground vinyl pools, without destroying the liner . . . . so no, that would not be a good idea. (They can sometimes be drained temporarily, but you have to hold the liner in place using multiple high-suction vacuums to do so.)

There's NO conversion to salt, other than adding salt. But you might spend $500 cleaning up the mess, which you have to do REGARDLESS of treatment method.

You WILL need a testkit. You WILL need a manual vacuum system and tools. You DO need to learn to manage the pool withOUT an SWCG, before you try to use an SWCG. We can help, but right now you're at the steep end of the learning curve.