Hi Josh and welcome. I wouldn't waste money on a grout protector with a dark coloured grout: only bother if you use a pale colour to prevent it getting discoloured. Good luck with your setting out and marking and remember to take your time, keep checking your measurements and don't forget to include the grout lines in your calculations.
I also am DIY but have done quite a lot of tiling as a DIYer I have used sealer in the past and seems to do a good job, water beads up on the grout. But I did a kitchen with Tilemaster 3000 grout and the sealer would not touch the grout it just sat there and beaded up so looks like the 3000 grout already has great waterproofing.
In that 3x3 kitchen + small extra area I left a 3-5mm gap and rather than use grout I opted to a (near as )matching Silicon, I would of had the skirting off but it was my daughters new build and she was not keen so they were left on. - picture
Don't mind me while I bump up some older but good threads. If you can contribute to the thread, go ahead. But if it's nothing for you then don't reply and it'll soon drop off the What's New page etc.
Worth linking to our new forum structure while I'm doing stuff:-