I tiled my fireplace with natural stone (including the vertical surface), my half bathroom, my kitchen, and am currently working on the guest bathroom. My wife will probably have me do our bathroom and the laundry room soon.
If your flooring is in bad shape, or uneven, you can put down (with screws) a layer of mortarboard or some self leveling compound (basically thinset mortar that you pour out and it will level the floor for you). This will give you a nice level surface to work with.
I use a QEP wet tile saw. It was about $70 from Lowes. Decent blades (Dewalt) cost almost as much as the saw itself, and are specific to the material that you're cutting (porcelain, ceramic, etc). The saw doesn't require a steady water source, like a hose. It has a small reservoir you add water to as needed. I use a 12" T-Square for marking straight lines to cut.
Before I did my first tile project, I had no more than just general common sense and a decent "handy man" background, learned from my dad who taught me guy stuff when I was a kid. I read a little bit about it, and jumped into it. Basically, mortar was wet in the bucket, so I had to learn on the fly.
When I buy tile, I buy about 10-15% over on the square footage. You'll have some mistakes, need some extras for edge pieces, maybe a spare if one gets broken in the future, etc. Unless you specifically need unsanded grout, I always get sanded. It's easier to spread into the joints IMO. I recommend a sealer out that you can mix into the grout instead of water so you don't have to go back afterwards and apply a sealant out of a bottle.
I wholeheartedly recommend doing it yourself. For $200 in tools that you can use for numerous jobs, you can do it yourself. You'll take more pride during the process, so the job will look better when finished. If you pay someone to do it, you'll see every little mistake they made and kick yourself for paying them.
PM me if you have any questions. I'm not a contractor, just a big time do-it-yourselfer. If you can think of it, I've done it in my own home, from electrical, tile, plumbing, lighting, drywall, cabinet making, etc.