The gateways can be used headless at any scale, they are open source, under the Mozilla licence and are not restricted in anyway.
However, it sounds like you wish to use the dashboard, portal, MDCB, etc, which are proprietary software and a licence is required (it’s how Tyk pays the bills for the software and support!)
If you would like to demo the architecture you just described, you just need to talk with one of the Tyk account team, they can discuss your requirements, provide a screen-share and quotation and then a short trial licence if you also want to try it out on your own hardware.
If this is of interest, then please send over your contact details to me at James @ tyk.io and I’ll get one of the team to follow up.
James @ tyk.io