Thank you so much for your posting! 
I've posted a couple of intro videos here on FMSOUP you can check out that show how to get started with the sparkjava framework and how to add a simple GET method to an existing service. I like sparkjava for lots of stuff. One thing I like is that sparkjava doesn't have all the "ceremony" of more complicated frameworks like SpringBoot yet lets you do things quickly.
Of course, you don't have to use Java, but I've been doing Java so long it was a natural choice for me. Plus, FMP has good support for Java with their JDBC driver and Java in general. Note that any JDBC code you write should mostly work on any database vendor since they all support the JDBC standard.
Java also gives you excellent 'packaging' options, like a JAR or WAR file. Using an IDE and "maven", you can easily create a "JAR" file (same format as ZIP) that has all the dependencies in it. Thus, your user, or you, only need to have Java installed. You can install a WAR file into an app server where it's always running.
Python would be my second choice using "Flask", but the web service programming language is a choice each developer or team makes.
Basically, regardless of the language (you probably already know this) you're just wrapping Java or Python or whatever code in HTTP method calls so you can call them from any HTTP-enabled application.
So, see if you can get the "hello world" intro service working. Then, you're ready to add some new method (aka, function) to do something totally new.
FMPDUDE-VIDEO: Creating a micro-service in a couple minutes (with FMP example)
Then check out the one that shows you how to add a new GET method and pass and process parameters.
I've posted more than 100 different programming samples that use micro-services and a FMP application on the FMI forum. Examples included Regular Expressions, date math, and more so if you need some project ideas, I'll happily post those.
Let me know how it goes for you. Post some code and we can all enjoy the experience.
I look forward to participating!
Will check back in soon.
Thanks again.
Stay safe.