For the water, there is a few different options. Most prefer that the engine "suck" in water, rather than have a hose "push" it in. I don't think it makes a difference, but it's easy to set it up either way.
Pull the intake hose away from the intake grate on the bottom of the boat. You can just shove a hose into this tube and hose clamp it around it, and it will work just fine. This is def the cheapest/easiest method.
You can also add a hose fitting, or a T, or any kind of valve combination that you feel like. This is how mine is setup and saves me from having to disconnect anything but the hose in order to hook it up on land.
Once you get the water hooked up, you'll want to run the engine for 10-15 minutes and get the oil up to temperature. (Thin oil is WAAAY easier to suck.) Chances are you are going to have to suck it out of the dipstick (unless a previous owner added a remote drain... but... that's unlikely.) This kind of pump has worked the best for me (I have it mounted to the top of a bucket and can reverse it to pump the bucket back out into jugs.) But you could also use something like this or this. Spend some time at the hardware store getting the right fittings and the right size poly-vinyl tube to feed it into your oil pan.
Suck as much out as you can, put on a new filter, fill her back up and enjoy the satisfaction of a job well done!
Former owner of a 1987 Supra Saltare. Current owner of a Malibu 23LSV.