newbie needs help choosing VPS plan and provider for a small experiment

Hello, I'm trying to experiment with setting up an asterisk / freepbx server. It's mostly for my own learning process, but if it turns out to go well and not be too tricky, perhaps it can be a solution for a small business that I work for.

I've been lurking a bit in the freepbx documentation and user forums, because the VOIP provider we are currently using has such poor customer support and documentation.. While of course we could easily switch to another provider, I read up a bit on setting up a server myself and would like to try it out just for kicks and gaining a better understanding of asterisk in general -- even if we don't use a home-made solution I'll still learn some lingo and how to ask for certain features from a VOIP provider, I figure.

my question: I'd rather not buy a server and set it up in my home office, as I don't have very reliable internet at home.
So - on to buying some server space.

I found this helpful thread - https://www.reddit.com/r/VOIP/comments/6908kr/vps_hosting_provider_success/ - and it sounds to me like vultr is a good option.

The business that I'm .. experimentally building this for .. is small. We are a team of 6 and we rarely would have more than 5 concurrent calls. We all work remotely in different corners of the US. The calls coming in are customers support calls and the functionality we mainly need was called a ring group by our current voip provider -- basically a way for a call to come in and get routed through a series of extensions if the first extension tried fails to answer.

all of this is to say -- this is very small potatoes - even if I imagine a future of growth for this small business, that would look maybe 20 extensions and .. the same number of concurrent calls. So .. can you guys guide me with some minimum system requirements I should keep in mind when I go to buy server space for this experiment?

for example, among the options vultr offers, what would you recommend for such a small business? do i need to spend 60 a month for a dedicated server to reliable call quality ? https://www.vultr.com/products/dedicated-cloud/#pricing