Both OXCE and OXCE+ can be installed just by replacing EXE of the compatible vanilla nightly installation.
At the moment, the officially-compatible nightly is from 2016-11-09... but since there is very little going on in vanilla, you'll be fine also with latest nightly.
There will be some missing strings, which you can download here: http://openxcom.org/forum/index.php/topic,5130.0.html
Note: in a few months, I'll move away from prototyping phase and will distribute OXCE+ with everything needed (same as nightly package), including extra strings.
There is a ruleset reference for OXCE, in the Extended-readme file.
For OXCE+ there is no single reference (yet)... I promise to write one, when I move away from prototyping phase.
However, all ruleset examples CAN be found on this forum.
I would start with the changelog, which is in the first 2 posts on my thread: http://openxcom.org/forum/index.php/topic,4187.0.html
It contains links to posts with examples, screenshots and much more.
Piratez and XCom-Files combined are using basically all features there are... I made new ruleset only when modders actually asked for it... so those are a good study material too.
OXCE/OXCE+ are fully compatible with vanilla ruleset, so your mod will work without problems on both OXCE and OXCE+ without any changes.
But, there are a few changes that are not exactly vanilla, however there are very few of them (less than 10)... like the reload cost you mentioned. One more I can think of is experience training... you don't get experience by just throwing flares for example, to gain experience, you must hit an enemy. All of these changes are however hardly noticeable by the players.
There is just one change, which is not compatible with vanilla and very noticeable by the players... the new OXCE lighting engine (light doesn't go through walls).
This will be fixed in the next OXCE release (3.6, coming very soon)... or at least Yankes promised it.
If not, I will fix it myself.
Finally, it may look like a lot... but it's really easy... and myself, Dioxine, Solarius, Yankes, Ohartenstein, etc. will gladly help you with the first steps.