I don't know that river personally, but have seen a lot of photos, and it looks like a good river for SUP. Not sure if that are any big drops in there - you probably don't want to run those as a beginner, unless you're an adrenaline junkie.

Make sure to start practicing on the easy stretches.

Use a PFD, helmet, leash with emergency release (if you have a quick release on your PFD belt, that works), good shoes, and possibly shin protection.

When falling off the board, try to fall flat - what goes up must come down, and if you fall in with your feet down, those feet will sink deep, and run a real danger of getting entrapped.

Plastic boards work pretty well, but are terrible to carry around, so unless the put-in and take-out are close to your car and there are no portages, you probably want to go inflatable.

Enjoy and please let us know here how it went

Go for small. I'm a bit over 80 kgs and also run easy whitewater, and I always use the shortest version of the inflatables. Makes the whole thing more playful and also more maneuverable. If you like getting the board half way vertical (standing on its tail), be aware that this is a quite unstable position on a 6" board. On a 4" board it's easier, but they are a bit less stiff. The MCIT from Badfish is a nice compromise, as it's pretty thin towards the ends, and thicker in the center, and it's a bit stiffer than a pure 4" board. They are a bit more expensive though, so you may want to get started with any short inflatable