Find the center of the wall & set your 1st tile there. The end cuts will match up.

You can't lay tile like a course of bricks.

Watch how to lay tile on you tube.

I'd pull the toilet first. At least the tank. If you want to get fancy you can put up ¼" cement board, a top "ledge" tile, and work your way down to a base tile. The cut can be uniform above the base run or you can do something I practically never do - lay it out and plan for success, to avoid a cut tile on your vertical.

Why stop there. Wainscot the whole bathroom hip-high. Then the halls ... down the steps ... stop at the mailbox.

Do the most out-of-the-way bathroom first for practice. The non-voters come to mind.

I've done both my bathrooms and around my Roman tub(not the shower stall/area). I just applied it to the drywall itself and used a polymer grout to keep out moisture and keep it from staining( big plus with kids). Polymer grout costs more and you will need to make sure to sponge over areas a few times more than standard grout or it will haze bad and it is difficult to get the haze off. Take your time and allow a day or two for your adhesive to dry prior to putting on grout.

I only did about 3.5' high around the bathrooms walls and up to the ceiling in the Roman tub area with crown molding at the top. It is not that hard but will be costly and time consuming, depending on what tile you select. I put the adhesive on each tile, as you will see, some walls are not plumb and if you put the adhesive on the wall first, you might not have enough adhesive to make the tile flush to one another and will have to build it up. When you grout with the polymer, do smaller areas until you get comfortable and eventually you will see if you can do larger areas,as it will dry quicker.

Also, don't cheap out, rent or buy a wet saw as that will make your job much easier and give you a good cut. You don't have to spend a lot but if you buy your own saw it is cheaper in the long run. I bought an inexpensive one at one of the big box stores years ago and have done many jobs with it. Get a couple floats and trowels and 5 gallon buckets. Don't look at them as an additional cost but as an investment.

Figure out a pattern you want on paper first so you can get the tiles you need on you first trip and adjust your count for at minimum 10% more tile than you need for the job.

It is not that hard to do and I have done many tile jobs in my home and other homes as favors to family and friends. I have done different patterns on floors/walls,which came out really nice but I took my time. If you are in the least bit mechanically inclined, it is not that hard and the first time you do it you will learn tricks for the next time.Good luck.