What server will be needed for the boxed version of the OS?

They are so individual - that I can simply answer you. "Beautiful and powerful"

The new OneBox OS product in its current implementation has proven to be generally faster and lighter than the old OneBox MVP (and earlier versions).
But, unfortunately, OneBox OS is not installed on the server BELOW THAN:
4 vCPUs (4 threads)
8 GB RAM
SSD drive
This is the minimum.
(For hetzner this is https://www.hetzner.com/cloud minimum CPX31-CX41, 13-16 euros/month)
Next, you need to look at the amount of data and what applications from the OS you have installed.
There are applications that require more cores and more memory.
I will give a specific example that affects small customers with online stores.
For example, you have an online store with 100,000 products, and you constantly (once an hour) recalculate prices for them (price recalculation).
OneBox MVP does this in ONE THREAD and takes a long time, so it needs 1 CPU core for this task. Even if you have a server with 128 cores, it's still in one thread.
OneBox OS does this in parallel in N threads in the background and immediately, without cron and other delays. If you have a minimum server for 4 threads (2-4 cores), then the OS will recalculate prices and availability for goods in one thread and it will be exactly the same speed as OneBox MVP. If you have a server with 20 cores - then the OS will perform this task on 17 cores in 17 threads at once - and it will be 17 times faster.
If we talk about the average for the hospital:
Previously, boxed clients had a server like 2-4 CPU, 4-8 GB RAM.
OneBox OS will average 4-8 CPUs, 16-32 GB RAM.

I will add:
In general, server requirements for OneBox OS can be described as follows:
If you have a server for 10-20 bucks a month, then you will have to increase it x2.
If you have a server for 50-200 bucks a month, you don't need to do anything, everything will work.
Describing prices, I was guided by hetzner.com

Good afternoon, tell me please
only 2 users,
total 7 automatic actions once per minute,
a total of 11 actions once per hour
total 400 items, daytime recalculation once an hour
I do not need super performance, the speed of work that was on the old box will suit me.
Is this server not enough?
VPS «OneboxVPS 2G»
CPU 2 Xeon E3 series processor cores available
RAM 2GB RAM
HDD 60GB SSD
Is it possible to install on the current server, and then check through the "Server Load Control Panel" whether it is enough for our needs. If there is not enough and it is not possible to work, then I will buy additional hosting capacities. Thanks to

On iron requirements to the server are clear. Are there any requirements, recommendations, wishes for software when ordering a VPS server hosting? Do I need any pre-installed software? What to choose CentOS-8 or CentOS-7?

If there is a choice - CentOS 8-stream.
If not - CentOS 7.
On 12/31/2021, official support for CentOS 8 ended, it moved to CentOS 8-STREAM.
At the same time, support for CentOS 7 remained.
Here's a joke from the CentOS team =)

https://1b.app/ru/docs/server_specifications/

Thanks a lot :)