Late on duty, but here eventually :o)
The cementitious v. epoxy grout argument seems to run forever.
Also, if the tiles are on a timber floor, then a latex grout is usually used (flexible.)
Everyone has their personal favourites.
This is a cementitious one that will do everything you need.........
Amazon.co.uk User Recommendation
Epoxys are not very DIY-friendly. I would stick with a cement one as in my link above. (Mapei is another one that tilers like.)
It wouldn't hurt to seal afterwards. Google something like HG Floor Sealer. (Cement grouts can be a little porous)
Ready-mixed are fine, but tilers tend to prefer powder since it's easy to adjust the mix as required. You just mix what you can confidently handle.
The other thing against Epoxy is that it tends not to flow so well as cement. Harder to poke into every cranny.
You could write a book about this. So many choices.
For you, you won't go wrong with the one in my link (or similar).
Grouting "floats" and sponges are essential too since you don't have to bother with "fingering" the joint afterwards. A good rub-up with a piece of sponge when almost dry and you're done.