Hi,
Your requirement looks quite clear and straightforward to implement. Both Windows and Linux are fine but my choice is Linux as it's a more stable os and de facto for this type of work.
Initially, I just need a couple of things you have to handle for me though. You should set up a linux machine, preferably Debian but any flavor is fine, plug the modems and provide ssh access with an account which has sudo privileges. You should also plug the SIM cards and share PIN numbers of each if there's any. Also, if you prefer any specific version of mysql please install it or just let me know. From that point, I'll handle the rest. I can even create a simple webpage displaying the stats and health of the modems if it's any use in addition to daily reporting to support.
I'm planning to use python to implement this. I'll also get help from some libraries though it's not certain which ones it'll be at this stage but pyserial will be definitely among them. So if you have specific needs concerning the licensing, e.g if you intend to distribute this solution commercially, please let me know so that I can choose, or not use at all, the libraries accordingly. I expect this to take 5 days, however because of my current workload I'll only be able to start on next Monday which means the deadline is next Friday, thanks for taking the time.
Best regards
Aydin