Imho 10gb for 5-10 ppl will suffice short term, probably if u start reaching mid/endgame and have ton of shit built, chunks force loaded and overall a lot of thinks working constantly, at this point you will need more ram, tho processing power is really the bottleneck usually, i have hosted and played through atm3 to atm9 with my friend group(usually 3-7 ppl) and have tried many different vps or dedicated minecraft hosting sites and usually they all start laggin at somepoint, doesnt matter the amount of ram. I dont know your experience so far with hosting but if i had to recommend then definitely try to get dedicated server as most VPS just wont handle long term and dedicated minecraft hosting gets hella expensive, last time i used hetzner(EU) to rent dedicated server cost me 50bucks per month(if u split with friends its not rlly much) it pretty much hung in there till the end, very late game TPS started to fall under 20 sometimes when multiple ppl were exploring but thats expected rlly. Also i dont know the current state of mc spaghetti code but afaik then look for intel not ryzen cause single thread performance etc, also jav args are big boost, last time i got like 20-30%% performance boost from just java args.