Hello there!

To change the starting units take a look at the race-specific-named odf-files in the odf\system-folder. So, if you'd like to change the Federation's starting-units, open the file named "federation.odf" with a text-editor and change the following just as you like it to be:

standardUnits1 = "fed_outpostS.odf"
standardUnits2 = "fed_venture.odf"

If you like to have a Defiant-class-ship as starting unit instead of the Venture, just make "fed_venture.odf" to "fed_defiant.odf". (This one is in the odf\units-folder.)

It should work. I say "should" because I did nearly everything but I never changed the starting units

To upload maps here, you've already found the right place. 
In order to post your maps, you have to use the normal reply-option and not quick-reply. There's an option called "Additional Options" and that's where you can attach files to your posts limited to a size of 1024 KB.

Enjoy! 

Indeed, this would change your starting-units permanently for every map and would also make your FO incompatible to other FO-versions. So you won't be able to play online any longer.

But:
In the map-editor there's a menu where you can change severals unit-stats like team and so on. I think that you could find there what you are looking for.
As I'm not that deep into map-editing I'll hand that over to someone who is from here on. 

I'm looking forward to get some time to check out some new maps.