Questions about hosting, multi-instance SAAS and scaling

Hello forums, during the past few months I have had trouble making the right decisions for hosting a project, I was hoping some of you could help me shed some light on the right path to choose… It’s a for-profit app with a pay for user/month model. The security of infomation was always a concern from the beginning, so each client have it’s own “instance” of the app.

It’s getting quite complex as well, so going from a multi-instance to multi-tenant is not possible, also we don’t update all our clients at once. Each client has it’s own dicretoy on the domain, so no subdomain (this is another problem), it ends up like this:

Right now the setup is realy simple on the server, I’m using meteor up, each client has it’s own port and a reverse proxy to the correct port, takes a few minutes to setup. I was happy with this this, but now with more clients, this won’t be sustainable for a long time. I was wondering a few things:

Is it possible to scale horizontally with a model like this, for instance could we use multiple servers but keep the “sub-directory” approach? Our clients generally have only a few accounts, maybe 30 at most, so load balancing for each client won’t be needed. However there is a limit to the maximum number of instances per server. We’d like to host more than one client per server.

This is probably not unique to Meteor, but I’m finding it hard to make decisions for a good stable architechture. Anyone has a way to deal with this? Thank you for reading.