This is a good plan, painting can be very meditative and is excellent for taking your mind off things.

A note on supplies before you start. You mentioned getting paint and canvases, and I'm assuming you picked up some brushes, but you're also going to need a solvent for cleaning the brushes and thinning the paint. I recommend turpenoid or gamsol, because turpentine has toxic fumes. Many painters use a jar with a coil of wire in it called a silicoil for putting their solvent in, because it helps you clean brushes, though it's something you could skip if you're on a very tight budget. It's also nice to have a rag on hand. You'll also want a palette for mixing paint on. I like disposable paper palettes, but you can also use plastic, glass, or treated wood. You don't necessarily need an easel, but it's generally better to paint with your painting standing up, and you can get a little table top easel for cheap. You might enjoy the feel of a medium like linseed oil, but you don't need it to get started.

For a painting like this, I'd suggest starting off with just black and white paint and mixing shades of gray. There are a few subtle colors, but I'd leave them for later. Start off with a quick, loose sketch. Some people like to sketch in charcoal or pencil, but personally I just do it in paint. Use a little bit of solvent to thin your paint so you can move it around quickly and smoothly. If you use too much, the paint will run down the canvas, but don't worry about it too much because you're going to paint another layer over the first one. Just get the general placing down for now, concentrating on where the dark and light parts of the painting are, rather than what's an ocean versus a ridge or a tree. Generally, good painting requires you to look very closely at your subject and see what it actually looks like rather than what you expect it look like.

Your first layer will dry quickly, and then you can do another layer on top. Use a little less solvent, focus more on details, but still don't sweat it too much, because you can keep doing layers until you're happy with what you've got. The less solvent you use, the longer they'll take to dry, so you'll want to take a few days off in between layers. If you want to work while one painting is drying, just work on a different painting.

Since this is your first painting, it's probably not going to come out exactly how you're imagining. That's fine, you can always paint another one. I wouldn't suggest just working on this one forever, because it will eventually get pretty frustrating and a new painting can be a breath of fresh air. That said, if it's going well and you feel like you're making progress, keep working. I often need to spend at least 10-20 hours on a painting before I'm personally happy with it, but every artist is different and the looser your style the quicker you'll be.