What VDS/VPS server configuration is needed for a remote SQL database?

Question

Database

Advise please a config of the server for a DB.

What you need for the database
* VDS on Windows
* Server with several databases (everything is possible in one, but it is easier in parts, because many directories are duplicated with slight differences for different clients / risk categories, attach someone else's less)
* Number of rows from 1 million up to 100 million in each database, the first stage will be from 1 database conditionally up to 100 million * 5 fields in the sources
* In select reports, 3-4 directories with 10-15 fields in total are hung on data from a large table (product, address, calendar, etc.) P.)
* Need easy remote access capability to add large number of rows from excel/csv to spreadsheets. Up to 10 million lines per month from 30-50 files in one format, one-time from the 10th to the 20th day of the month. Accordingly, we need a way to check the correctness of adding by the number of rows / amount added, either automated or by hand through select at least.
* Setting up backup of sources / a large table + the ability to save versions of directories to an archive once a month or two, you can do it manually, there are not so many directories

For the "client" part and studio
* Ideally, server management studio or an analogue for a simple interface for checking data and creating /edit queries
* For the user, visualization is needed - the ability to pull out your report (select / view or pre-calculation table, depending on the severity of the report / server capacity) into a tabular report / chart data by its categories with the ability to export to excel or csv. Now 1 (one) user works several times a month in Tibco, but you can also have an analogue - power BI, tableu, clikview, cognos, etc.

Future
* In the future, you need to develop the visualization block, add about 30 graphs with dynamics in different sections in absolute values ​​and shares (category sales and brand share) + a dozen calculated indicators from the report, for example, distribution%, etc.
* In the future, it is possible to increase the number of users, so you need either a differentiation of rights, or different databases for different users. The user has access only to the report, not to the database itself.
* Own server is not planned, immediately VDS. It should be possible to easily migrate to a more powerful configuration if needed.

Questions.
1. What Win-server configuration will be enough? What is the percentage / memory / ssd + hdd? (you need to choose a hoster, if you can advise a normal win-VDS hoster - it will be absolutely fine)
2. The database is planned for PostgreSQL, MySQL, SQLite, MSSql - what will be better for these tasks? Free is welcome, because while this is a test. Next, we can switch to a license.
3. Do I understand correctly that WebDav is enough for remote access to manually / automatically add data to the database from Excel / csv?
4. What is the best way to backup a database? Free is welcome, because while this is a test. Next, we can switch to a license.

Answer 1

The main criterion is the load on the base. If you have several users, then any VPS that meets the requirements for the system)
In general, hire an architect. Or just a smart person. A DB on Windows - as that sounds strange.
And be consistent. MySQL\PostgreSQL - ported to Windows, not native to it. They will work, but...
It's logical to hear that you want MSSQL under Windows, but you don't even mention it...

Answer 2

A classic question that begs for advice about hiring a system architect, DBA, sysadmin, and the list goes on. A toaster will not replace all this.