Sounds like an exciting project @brightoibe!
Bahmni is more complete solution.
It includes things we don’t have in the OpenMRS Reference Application such as drug prescriptions, lab orders, multiple configurable patient dashboards, and appointment scheduling.
Bahmni also covers all of the typical workflows in a typical health facility, e.g. it integrates an ERP which can do stock management and billing (and has lots of plugins for even things like HR management that you’d never want to end up building yourself), as well as Lab and PACS systems.
So you get a lot more out of the box, and it is a better solution for the “EMR meant for a general hospital” use case. The basics of implementing Bahmni rely on a lot more configuration via JSON and SQL, and less outright programming. Though you’d surely need to do some development work to add some features there too.
With the Reference Application you would certainly be more consistent with what Uganda has been doing (as @ssmusoke describes), and since it supports HTML Form Entry you’d probably find it more familiar. The dev community for the refapp on these forums is much more mature and more talkative than the Bahmni ones, which are newer. (You can see Development versus Bahmni for example.)
I would suggest you take a close look at the https://www.bahmni.org website, and its Feature Guide. They would give you some background as to what Bahmni is and how it differs. (Under the hood, Bahmni is running OpenMRS though.)
Disclosure: I work on the Bahmni team, though I’ve also done lots of work with the Reference Application.
Take brief note of this work that I’m trying to organize: "OCL for OpenMRS" application
This will probably be relevant for you in a few months, but not yet today.
Back-end modules need Java, Spring, and usually Hibernate.
The current reference application code uses a non-ideal mix of Groovy templates with Java controllers, along with some Angular 1.x code (but also some older JS code as well).
Bahmni is mostly written in AngularJS 1.x.
Going forward there seems to be a significant movement in both projects to use ReactJS for new front-end apps.
On the topic of Bahmni vs the Reference Application, Bahmni allows you to go further with “just configuration”, e.g. in addition to the data capture forms you can also set up dashboards and patient queues.
In the big picture your team will definitely need to more than just defining forms, but not everyone needs to.
And, per #3, we’re very much trying to move away from JSP/Servlets, and towards HTML+JS+REST technologies wherever possible.
See http://radar.openmrs.org/ for lots of recommendations of what technologies to use. (“Adopt” means definitely try this. “Hold” means stay away.)
+1 to everything that @dkayiwa said.
+1 to 95% of what @ssmusoke said. 
Whatever distribution you choose, definitely you want to start with the latest version, and you want to have a plan to take regular updates, so that you can regularly get new functionality and bugfixes. (Your upgrade cycle might only be once per year, though modern CI/CD techniques could help you speed this up, but definitely plan for upgrades instead of thinking you’ll pick one version now and stick to it forever.