Well, there they are.
Automaton, Gremlin, Lich, Valkyrie and Ryu. They're my top tier.
This is hard for half of them would be fun to have in a harem, by since you said only five I would pick
Hellhound
Kikimora
Ren xiongmao
Pararoh
Inari
Understand these are in no order as to how would be primary to secondary
Gnome, Demon, Medusa, Kraken, Slime Carrier
Lilim,Lizardman,Chesire Cat,Raiju and Vampire
Holstaur, Hobgoblin, Inari, Jubjub, and Thunderbird
With a harem like this, will I live?
I'm going to choose an apsara, a wight, a kejourou, a demon, and a shirohebi.
Not exactly wholesome (I'm very concerned about the wight and the demon,) getting a harem with a shirohebi has a 90% chance of getting killed, and I'm still not on board with the immortality elixir thing, but at least I'll be very happy with the constant cuddles and love from the beautiful ladies.
All I need is probably some words of encouragement to survive the living hell that is the harem, though.
Mindflayer, Doppelganger, Phantom, Nightmare, Dark Valkyrie
The dynamics herein, whether sexually, emotionally, magically, or spiritually, would easily allow for any desired dynamics to be explored.
shirohebi, hellhound, will-o-the-wisp, manticore and vampire.
never a dull moment while living with all of these mamano together. real question is will i survive?
Haktaku,kushala (fan made),kikimora,vampire,and shirohebi
Now will I survive with this harem probably not but it's sure as hell gonna be interesting.
Atlach-Nacha, Mindflayer, Night Gaunt, Wendigo, Shoggoth.
Fuse with all five and become the ultimate spider/squid/slime/beastman/eldritch demon! Then turn the world into an abyssal mamono realm. It would take some getting used to but I could still turn back to human so that's neat.