I just made a couple threads about this lol.
Here and
here. Some good responses, so worth checking both.
A few points:
-You can cast every single Conjure X spell with Wish, just 3 levels after you get that strong 14th level ability anyway
-Conjure Minor Elementals is your best bet until then, you're basically guaranteed a crapload of mephits (ask the DM if they can each summon more with their "Variant: Summon Mephits" ability - an 8th level slot will give you 24 of them...
-In general, always opt for the lowest level CR when casting these spells, not only because you get more 'free' temp HP this way, but also because it prevents the DM from fking with you and picking something weak (it says "or lower" and the DM gets to pick so...)
-Position them wherever they will get the most opportunity attacks, they can all occupy the same space if you wish, but I'd spread them into a moving wall that prevents enemies from reaching you
-Blindness/Deafness is a good spell to take because it gives all your pets advantage on a specific target and doesn't require concentration
-Counterspell is good in case they cast Dispel Magic
-Any 'forced movement on their turn' spells/abilities like Turn Undead will provoke many opportunity attacks
-You're gonna piss off the DM and other players by slowing down the game, bring extra dice and have your creature stats/HP handy
