[Andreas]

Originally Posted by addamroy

I already sent an email to the email in the readme but didn't get a response back.

Maybe I missed it but I don't rembmber any email from you?

However, in the description it says 'partly compatible with 4.0.x', what exactly do you mean by partly?

Partly means that it does work, but that it is not fully compatible
Eg. expect problems in some usae cases (like editing a template that has template modifications, modifying a .css-template with TMS, saving a template-modification that contains one half of a conditional, etc.).
Apart from that it does work (eg. importing Add-ons that contain TMS data and having that applied).

Is the sitewide footer link really necessary?

Yes
Developing software costs a lot of time - the link compensates that.
If you do not want to have a link you can purcahse a branding-free license for 15 €.

Could this be expanded to include the creation of custom templates ?

TMS is not care if templates are "custom" or not.
For you usecase I'd sugest to create your own Add-on, create your custom templates for that Add-on in MASTER style - then they will automatically appear in all styles.
But that has nothing to do with TMS