Wall tile questions

I'm working on tiling the wall of a wet bar area. My plan is to do white subway tiles. The wall area (minus cabinets) is about 25 square feet. I have a couple questions.

1. I had to cut 4 holes in the drywall to run electrical wire to various parts of the cabinets. I cut the holes and then put the drywall pieces back in and fastened them to a 1x4 piece behind the wall using drywall screws. Do I need to tape/mud the gaps between the drywall piece and the wall? They are pretty small but as you know drywall pieces go back in smaller than they came out since you lose some in the cutting process.

2. For the tile I keep reading online people saying don't go to HD/Lowes for tiles, go to a proper local tile shop because they will have higher quality tiles. If my plan is to just do 3x6 ceramic subway tiles, how much does it really matter that I go to a tile shop versus HD/Lowes. I plan to buy lugged tile with 1/16 spaces.

3. Any other advice on doing the tiling?