You can have any combination you want, be it 10 fruits or just one. In fact, the best nectar ever made by Nectaux consisted of only one fruit: Cherries. I picked this up after fully completing the nectary challenges, it was worth just over $6,000 at over 6,000 years old, now it is worth $10,777, sitting in my basement on a 'The Nectaux' rack.
I have a few combinations, though I'm still experimenting, these were all initially worth between $250 and $300:
(upgrade used: flavour enhancement, process: extended nectaration)
*4 avornalino grapes, 4 cherimola blan grapes, 3 renoit grapes.
*4 flame fruit, 3 life fruit, 3 plum.
*5 avornalino grapes, 3 life fruit, 3 cherries.
*3 meloire grapes, 4 cherimola grapes, 2 renoit grapes.
*1 life fruit, 1 flame fruit, 2 cherries, 3 cranerlet nuala grapes, 3 gralladina fran grapes.
One last point, one of the tips at the startup told me that nectar ages and improves in the deepest depths of the basement. Would it be correct to assume that the deeper your basement is, the more the nectar stored there will improve?