Best way to host Unity2D Game online with multiplayer

I wondered in anyone here had any experience with making online multiplayer games with unity? See ive been working on a single player game for almost a year now, a 2d platformer and I realize now that ive bitten off more than i can chew making it all by myself and im almost out of money while being no where near finished.

Anyways i had a really good idea for an online multiplayer game, with maybe 4 against 4 using the same mechanics ive been working on and wondered what was the best way to go about it, i had a few questions i thought id ask here first.

how should i host it, should i buy a domain and use a website builder and a server host, how much would that cost to allow 100 people to play, also is http://itch.io any good?

would it be possible for people playing the game to host games themself

anyways ive not got much experience with website building and ive never attempted any online functionality before so any advice would be greatly appreciated, has anyone here attempted anything similar?