I think you need to think about your priorities and lifestyle. These obviously change over time.
We have been living in our house for 18 years and in that period have extended 3 times. It started off with 4 bedrooms, one of which is tiny and has always been used as a study, and one of which is en-suite. Downstairs was one big room in two distinct halves, a tiny kitchen and an even tinier utility room and a funny sort of nothing space which I remember the estate agents called a "rear lobby". Also a double garage, half of which was integrated and half of which wasn't.
When we first moved, we had a toddler and I was pregnant. My top priority was a kitchen we could eat in. I also wanted a second reception room so could separate TV and piano. We therefore converted the integrated garage. The front became a separate small reception room (which was a play room/music room). The back joined onto the kitchen and utility room to make a bigger kitchen so we could eat in it, and the rear lobby became a new utility room.
Phase 2 became important as the children became teenagers. When we had guests, the two girls shared a room but that was less manageable when they became teenagers because of bed sizes. We therefore built another bedroom over the garage, which is the spare room. I'd have liked this to be ensuite but we had to make it smaller than I wanted (planning permission) so it isn't.
Phase 3 happened because we wanted more space downstairs and I wanted the children to be able to have a separate room downstairs so that could have some privacy with friends or boyfriends without taking them into their bedrooms! The music room became a small sitting/TV room, the piano moved into the main sitting room so that became the new music room, and we added a conservatory to the back of the sitting room, and that became the new sitting/dining room.
The point I am making is the house has adapted and grown with us over time as our needs have changed (and as we have been able to afford it). I think we had anticipated that we would move house and we considered this before phase 2 but rejected it as our current house is in a v convenient location and moving would have been far more expensive.
I think we have now exhausted the possibilities for extending, but I anticipate that we will change usage round in a few years when the children leave home.
In a perfect world, I would have a walk-in larder and the spare room would definitely be en-suite (much more convenient when elderly parents are staying, though sadly we now only have one of those left). A walk-in wardrobe would be a very long way down my personal wish-list.