Roger raises another excellent point --- what you start with may either drive or change with a larger lineup of glass.2. If you plan to have 5-6 lenses at some point ..then adding a 21 or an 18 on one end and a 90 on the other increases your range.
In my case, I prefer at least two bodies, and regularly carry 5 lenses with them: a 12 for vast interiors, 21, 28, 50 and 73 (mostly for people and artistic isolations); the 21/28/50 are my workhorse trio. I own an old, beat to crap 35 Ver3 Cron and love the way it renders, but virtually never mount it! At the end of the day, my 73 Hektor is a unique optic and in truth I'd probably be better served with a 90 instead for most travel/street situations, but the look it generates is so pleasant I continue to carry it.
Cheers,