Hi Cjamum,
Sorry to hijack your thread. Was just browsing and came across this so thought I would respond to you as we have gone through this ourselves.
You will probably find you will need to screed. We used 600x600 tiles too and had our own tiler lay them throughout the main areas of the house post handover. Our builder (we didn't use MJ) did the wet areas as part of the build but all living areas we did post handover including tiles and carpet.
when using such big format tiles they need to be glued on to a perfectly level base and a house slab isn't level enough. Possibly fine for normal sized tiles but with 600s it needs to be near perfect otherwise you will risk having them crack later on.
We were lucky that our builder actually gave us our house for a week mid build so our tiler could come in and screed before they started on the main fit outs like the kitchen. You want your kitchen to go on top of the screed if you can otherwise all your heights will be thrown out. If you don't, then make sure you allow for your cupboards and kick boards to be installed at a raised height so when you do screed you don't lose this height. It's also very messy so you don't want anything getting ruined.. 15 or 30mm in our case can be a lot to lose if your bench is at say 900mm off floor and then becomes 870mm. Also your skirtings, if you're screeding post skirtings have them tacked on so your tiler can remove and you will need to put them back on and paint once tiling is completed, or in our case as we had already screeded, we had our skirtings put on (so the builder could paint them), 15mm above floor height to allow for glue and tile so our tiler could slide them under the skirtings for a clean finish.
We screeded all the areas but not the carpeted bedrooms as we simply could not afford to screed our whole slab, however my time over I would definitely screed the bedrooms, so we do have a lip from hallway to beds, but we did screed the home theatre and study that run off the main entry hall as recommended by our tiler so the carpet runs flush to the tile in the main entry.
So once the angles were put on in the laundry and bathrooms by the builder's tilers, our tiler then based his levels off these so they all run evenly flush from hall to laundry and bathrooms. Our doors did all need to be shaved, however apparently for us it was about 30mm so our builder wouldn't shave them as they said that was too much and our doors could warp over time and bend so they ended up cutting above all the doors and actually raised the door architraves 30mm so they didn't shave any door off. we have 10ft ceilings and already had the 2340mm doors so it actually worked out well for us as the doors are even taller looking, but was a big job. We were also lucky we screeded mid-build, because this wouldn't have been possible post handover.
Anyway, not sure where you're up to but if tiling yourself post handover, perhaps get MJ to screed for you before the kitchen if you can, unless they will allow your tiler entry to do this for you - if not then definitely keep the height changes in mind.
Also, if using porcelain, be prepared for the cleaning. the wax and haze on some of them is horrendous. I am still to find a way for streak free so if anyone has any ideas please let me know. I use HOT water and vinegar, which is ok, but still in the light the streaks are there in places. I can't polish on hands and knees as we have I think over 150sqm of tiled area...
ANYWAY, sorry again for the hijack, but having done this ourselves we learned so much from the experience that I don't think I would do it myself again, but hope this helps you a little in preparation for your tiles.
Good Luck.