I added HTH stabilizer granules and started with liquid chlorine, because it's what I had. I don't think there's a difference. Only thing is, the amount of granules needed is so tiny that you need a kitchen scale to weigh them correctly. You're not adding by the jug like you would with a pool.
Sure, that works great. I think the dichlor method is because it's often easier to get dichlor, and you don't need much. If you don't have a pool, and just have a hot tub, then a small bottle of dichlor lasts a long time. When I got our 290 gallon inflatable spa, I got a 2 lb bottle of dichlor off Amazon for $20. After 4 rounds of opening (to 30 ppm CYA), I have over half that bottle remaining.
If you already have CYA because you own a pool, then may as well skip the dichlor and use straight CYA. As with a pool, you'll want to put it in a sock or similar, and it will take a couple days to dissolve. One of the advantages of dichlor is it almost instantly dissolves.
Since we're setting up our first pool, it's likely that in a year or two when I finally use up the dichlor I have, I'll just use straight CYA since I'll have it on hand for the pool anyway.