Tap water is much easier and a heck of a lot cheaper, so why not go with it? I guess if you have some nasty, local tap water you might want to use some RO. But, the water params will tell you that. From a tap water perspective, you'll mainly need to know the KH and the GH. Let the tap water sit out for 24 hours for any residual gases (e.g. CO2) to leach out. The KH and an assumed CO2 level of around 3 should predict where your PH is sitting. If not, that's something else to look further into.
As to ongoing tests once you get the plants going, you'll want PH (so you can bounce against KH to determine CO2 levels), nitrate (NO3) and phosphate (PO4). Don't bother with an iron/Fe test kits.
As to brands, there's lots of opinions out there. Most seem to feel that any ph, kh and gh kit will work. Lots of differing stories on the NO3 and PO4 side. I've had good luck with my first Red Sea PO4 kit (you want want that'll measure at the low range, 0-2.0). As to NO3, I recently stepped up to the more expensive LaMotte line, as I had 3-4 other kits die very quickly on me. I've read some decent things about the Sailfert kits. I do believe that they do work for FW, even though they typcially sell for SW. But, I've got no presonnal experience with the line.
Welcome and good luck!