The SW sample pots are huge, get them to colour match a smaller one. If you paint a couple of cardboard sheets you can stick them up in various rooms to see it in different light

If you were still looking for some warmth and a little variation look at Dulux Natural White or Casper White Quarter. Both work well with Vivid White, so will still work with your trims and kitchen cabinets, however will provide a slight difference between your walls and trim work. In saying that there's no problem in using Dulux Vivid White for both walls and trims.

I think you really can't go wrong with Natural White, but I would try continuing the Grey Pebble and just being mindful of introducing surfaces that will reflect the light such as a big mirror, a large light coloured print and some light timber furniture. And of course it's a great opportunity to introduce some amazing lighting!

Our church underwent a major renovation a few years ago, I think carpet is the way to go - good for all weather types and absorbing sound. Our church went with a commercial grade carpet - dark blue with faint white dashes, which has held up very well considering the heavy foot traffic. Our church had a committee to plan the renovation, it took months and also involved people in the congregation who had interior design qualifications which really helped since it’s the people who worship at a church would know what works best. By the way, I don’t think it’s a good idea to raise the rest of the flooring so that it is all one level, it’s hard for people towards the back of the hall to see the speaker and what not at the front. All the best with the renovations!