RE: How many aircraft are too many?
If you're single, there is no such thing as too many -- right up to the point of bankruptcy.
If you're married, you have an automatic limiter -- she will determine how many is too many -- listen carefully & avoid bankruptcy.
My Dragon's tolerance limit is 10, in ready-to-go configuration -- they live indoors & are hung from various ceilings. The number of spares, repairs, kits & half-builts is somewhat indeterminate, depending on how many you can hide at a buddy's home. I have at least a dozen in that state, but occasionally the Dragon breathes fire & the number subsides somewhat. It seems that an all-up inventory of ~ 25 is the outer limit for me.