I'm going to tile my house and going to use 20" and 6" tile pattern. With this pattern, do I need to start in a specific place, or can I start in the bathroom and work my way down the hall through the kitchen and dining rooms?
I think the most important room should have the pattern centerd but you also want to consider all areas so you don't end up with a real lopsided look down the hall or 1/2" strip in front of the tub. You just have to do the homework.
With that big a tile you need to do some research to see if that floor will even be able to be tiled. Not all floors without some extra work can be.
There can be 0 floor deflection in tiles that big, There needs to be at least 1-1/8 subflooring and underlayment.
There can be no partical board or 1/4 underlaymant.
I agree that the main room should be considered first. Maybe I'll lay the pattern out through most of the area to be sure. Also it's a concrete slab that I have so I assumed that I didn't need an underlay. Am I wrong?
Sealant will do nothing more then stop material from falling in the crack.
If your going to install tiles that big then there's a very big chance it will crack right where that crack is sooner or later from movement. http://www.schluter.com/media/articles/fhb_art_tile_floor_us.pdf
This seems like a big job and a lot of questions. If this is truly going to be a DIY job then the only saving grace might be is to measure all rooms walls to walls use long level make shore your all level up to par, put your pattern down first on the floor with pencil all your lines where your tiles are going were your cut peaces are going you always want to work your way out not in so you don't end up having to walk on the tile before they dry.
Do one room at a time.