I know RabidBat you probably hate me right now, but I'll impart my knowledge on the topic anyway as I've been running a server for a while now and have some experience on the matter.
In terms of RAM, I see normally between 2 and 3GB of RAM usage for StarMade - this does vary a bit but not much, I allocate 8GB to StarMade and it's never reached that ceiling yet - in the last 12 months we never peaked above 30 players, but previously we had 150 players and even then the RAM never broached 8GB.
CPU is a bit harder to gauge - I have a 4 core, hyperthreaded Intel E3 1271 V3 and it seems to handle the load fine - but it does have spikes in CPU for short bursts, depending on what people are doing. I don't think a faster CPU probably would not help that much - not enough to warrant the cost.
Disk I didn't think would be that important, but it makes a big difference when backing up or updating. Running on a Samsung EVO 840 120GB there was no noticable bottleneck, but recently I had to temporarily move the game data to a back mechanical drive in preparation for a capacity upgrade on the SSD (that's another issue - 120GB is not enough for a server with a large universe), and during that time there was noticeable latency to all players when people joined - I never bothered troubleshooting this to work out the exact cause as a few days later I had my new 480GB SSD and moved it back and the issue evaporated.
When updating StarMade, it makes a backup of all data - and with slow disks this takes a long time if you have a large universe. Like about 90 minutes on a mechanical compared to 20 minutes on an SSD with 100+GB of data. It also means you need to have capacity of around 20% on your drive to perform StarMade server updates (game data seems to compress well).
Bandwidth is going to be the key area of concern when running a StarMade server in countries like Australia - where my server is hosted.
It's mainly the upstream which gets hammered - and in Australia they meter both upload and download. For 20 to 50 regular users, look for a 2TB allowance or more per month - and you want to make sure you have a host that can handle 100Mb/s upload or more which isn't just burst. There have been changes to StarMade to try and lessen the bandwidth requirements, but It's still fairly heavy.
DDoS protection is something you should consider as well. Most Australian hosts DO NOT allow gaming or IRC traffic as they attract DDoS attacks, so you need to carefully read their terms and conditions - I've had several hosts shut me down because I was DDoS'd.
I use
Dedicated Gaming for my hosting, and they're absolutely awesome (I have no affiliation with them - they just deserve credit). They expect you to know your way around a server yourself, but have solid, proven DDoS protection (BlackLotus, Staminus and locally NSFocus) and seem to have a 1:1 contention ratio on the bandwidth (meaning you always get your port speed). I customised my server to suit my needs (added a few SSD's and upped the bandwidth) - so they are open to customising the hardware. You'll also probably get a better deal by telephoning them - they were flexible with prices when I called and negotiated my deal.
I pay $404 AUD a month for my server with Dedicated Gaming, that's with 3 SSD's (one for the OS, one for StarMade and one for a Minecraft server), a 2TB mechanical SATA (used for daily backups), 32GB ECC RAM and 3TB of bandwidth using a 100Mb/s port using an Intel E3 1271 V3 CPU. I run a website, IRC server and forums on my box as well, so if you were just running StarMade you could get by with a lot less.
Recently Dedicated Gaming updated their plans for dedicated servers to be all 1GB/s ports, and lowered their prices - from looking at their offerings today their DG-Box1 product should suit your needs at $250 per month - if you are just running StarMade on it.
Good Luck!
EDIT: I should add, that if you want to check if a host does offer proven DDoS mitigation (and you should never take their word for it), check their AS peering on he.net. this is the report for my
provider- as you can see it has black lotus and staminus shown as a peers - which indicates they can readily redirect traffic to them via BGP routes.
