If you can score and snap your tiles then you are using crap tile.
Any tile worth laying will have such a hard glaze that it won't score/snap.
Also can't score/snap natural stone which is what I usually lay now.
I've done about 20-25 tile jobs now. I'd say that for a small project like yours you can get away with one of the cheap wet saws from Homie Depot for $90 or so. And then when you're done you can toss it on Craigs List for $70 and recoup.
Or get a 3.5hp 10" overhead wet saw like me and go to town.
For rounded cuts or quick tiny cuts get a cheaper angle grinder($30 at Lowes) and then pick up a cheap 4 1/2" diamond blade for it. I've used the same diamond blade for years now. It'll be a dry cut so the dust will be great, so you do those outside if you can. A great tool to have for cutting a hole out for the toilet drain. Remember the cut doesn't have to be super pretty since it'll be covered by the toilet.
Use spacers, they come in a bag of 100 or like 3 cents and are cheap insurance that it's done correctly. I still use them for some jobs.
Try to be anal about the water/thinset ratio. You can eye it up but to get optimum consistancy and workability you'll want to follow instructions.
Being a concrete floor you have to be sure there isn't a seal on of concrete that will inhibit the thinset from sticking. There is an acid wash that you're supposed to scrub on the floor before hand but I can't remember what the mixture is.
Tiling is simple if you double check everything before actually slapping them down. Even if you put them down and one or two are not straight or level, you have a day or so before they are really secured. So you can pull it up or break it out, scrap off the thinset on the ground, and do it again.
Always hide your cuts.
Give me $5
Seal the grout after it cures.
Lay the tiles sober-ish
Be patient too.