First question is about the present wiring. 120 or 240 volts? That S200 filter is rated at 44 GPM so you want to stay under that. The Hayward site leaves a lot to be desired for getting detailed info on a specific pump but on a quick look I'm thinking of a 1/2 HP full rated, something like the SP2600X5 single speed so you are right on your thinking about the 1/2 HP. Then we get into the two speed pumps for more $$$. As for wiring the thing in, that's easy if you stay with the same voltage but if you change then things get more complicated. I think that model I mentioned is what Watermom has for her AG pool and the suction for vacuuming is quite adequate. I've got a 1 HP Superpump for my 22K IG and it's 14 years old and still going strong.
Al