You should stick with what you know. If you are comfortable with LAMP stack then you should keep using that. I am assuming that a good chunk of your work comes from maintaining what you wrote for a previous client and for these type of jobs it is best if you follow a standard (which you define). That way you won't have to think (as much) about your code before you start to make any changes to it.

A vps provider like digital ocean or linode can certainly be a good choice, if you also take care of hosting. With them you could set up a proxy server (I prefer nginx) in front of the apps for your clients and serve them all from a single vps. The traffic of 10-1000 of users is not too big but if you feel that performance of an app is degrading you can always migrate it to a managed hosting service like heroku. That way you can also charge different fees from your clients based on how you are managing their applications.