Saurabh piracy happens everywhere, you cannot stop that. Based on my experience, those who want to have their own swiggy kind of stuff, never think about using the cloud version.
1) It happens on every script and people will live with that. For this one reason, people never move to the cloud version.
2) You can ignore them or provide paid tech support for such cases
3) This again happens on every script, you have to concentrate on 2000+ paid users and have to find how to make a recurring revenue.
Obviously, 1-time cost never will be sufficient for development. You have to charge yearly for script as I said previously. But for people who paid for extended, that can be one time. So you will see lots of conversion from regular to extended and then many retaining regular.
And you can offer multiple plugins, multiple themes etc and make money out of it. There are tons of plugins you can do which are missing right now to make or utilize foodoma.
Example:
Product shopping feed for google
Conversion pixel
POS integration
and many
also you can release single restaurant app for foodoma
I suggest reconsidering before investing time in SaaS as you will not get the return you might be expecting now.