For example, I want to create a server with a predictable online ~300(single map, because it`s a RolePlay server). Is it possible without lags? And what VPS/VDS host should I pick? I`ve found one(dedicated server), there`s toooooo much RAM and SSD capacity here, but CPU seems good. Have a look: Intel i7-7700K 4c/8t - 4.2GHz /4.5GHz 64GB DDR4 2400 MHz SoftRAID 2x450GB NVMe 250 Mbps bandwidth BTW: What performance boost should I expect when switching from SSD to NVMe? I don`t like MCPE game hosts, because they don`t provide full-control to your system. And also they can just turn off ur server, if it`s getting DDOSed. And the very last thing I wanna ask: what do you think about GTXGaming host? It`s quite cheap and has many advantages, such as great CPU(4+ GHz), PCIe SSD etc. They have Minecraft: PE offer(find on their website), but I`m not sure about their customer support. Maybe someone already used GTXGaming?
What performance boost should I expect when switching from SSD to NVMe?: Should not even be noticeable and after https://github.com/pmmp/PocketMine-MP/pull/1895 is merged: None at all. The CPU looks good, and as you said too much RAM and SSD capacity. 300 players will be hard for the server though, but if they are all in one world it might be fine, some people have reported such crazy player counts working out.
You should also consider your geo location and where you expect the majority of your users to come from. Get an additional IP for eg UK to improve lag to that region