I agree with you the pillars are unfortunate. The replacement tiles will stand out no matter how close they come to matching so you're better off making sure they are clearly different so the gray one is better. Putting busy mosaic tiles could look nice but will interrupt the flow between rooms which I'm guessing is your problem with the columns in the first place. You will need to create a dextrous solution to tying into the 2x4 wall on the left side but I think it can be done tastefully- maybe beveling it back once you get past he end of that wall.

I love your post, there is a blueprint and you are giving out details and whishes witch is making it easier for all of us to help you and your family. This floorplans reminds me a bit about my uncles house. here are some of my thoughs witch you may/or may not use. I am not sure about the NSEV directions which have a major influence in building a house. Parenting so many kids also influence the house and the lifestyle in the home. I would maybe add, or rebuild an ancle to the house prevent from wind on the terrace. Commidded as you sound i would go all in with all of your wishes. I think a big master bathroom is needed to be used as a place to relax with so much to look after. I dont now if your coing to use the door in the lundry room or in the pantry most. I thinks its best to have your garrage entry close to the pantry and kitchen. A open kitchen is also a big decision when you have so many young kids. I would maybe add a breakfast area in the kitchen. SOme other things to consider is maybe the entry and the long hall way. I think you and your family might be a bit tired of the loong hallway. if possible i would switch the entry and the office. to make the entry in to the livingroom, if le librarry is going to be used as a familyroom. A toilet should always be placed near an entry to the house. And an extra toilet is only for u to clean along the way.... I you are looking to expad the family i would maybe build a playroom in the middle of all the kids rooms. At my uncle ealier house theay had a combined office space, guest room, playroom to combind a space for all of the children and their friends to be in. As far as going to design in your home can also maybe influence the layout. I think wood floors or tiles depend on style. I Personally prefer laminet wood floors in the kitchen and entry, but you are to buy some lovely tiles now a day. Pleace ask for a new blueprint suggestion if you are up for some changes. good luck.

after watching my daughter and her husband agonize over the way their expensive timber floor has not held up well after 3 years, I would recommend tiles/wood look tiles with under heating. Their beautiful warm expensive floor looks like it always needs a clean and polish, not from neglect, they have cared for it well. One of the boards now has a slight and painful moan when it's stepped on :-( I grew up in a completely wood floor home and although it looked wonderful, my Mother hated it. ....and the mats ! Wood is a lot harder to maintain than tiles ,(no matter what the die hards say) the modern wood finishes are much better than they used to be.... But a piece of wood is rather arty no matter what it's used for and it does demand to be loved and cared for.....and if something goes wrong it's a lot more expensive to fix than sand and cement. Ultimately you have to be happy. BTW underheating tiles is warmer than timber :-)

Get rid of that bulky corner pantry because it dominates the entire kitchen visually and floor space wise. A well designed cupboard pantry flat against the wall will hold all you need and free up floor space for a larger counter/bench or possibly an island if you wish.