QUESTION Best practice to integrate own business logic in GS

[Bigin]

It depends on the logic of the script/application, there's more than one way to achieve this, I would move the logic into a plugin and put View and Controller into theme (you could expand it by having multiple View/Controller files). But, sometimes, if I want more control over routing, for example, I put my Controller and Router with in the plugin, it allows you to hook into running processes.

As you will probably have to handle a lot of data, I would use a proper database on your place. Databases can handle very complicated queries, and with ORM it gives you the ability to manipulate data in a very friendly way, etc...