I'm a defense/security geek, so I feel comfortable saying: The operative unspoken here would be try to use common weapons and such - in reality, every force seemingly fields its own pistol, rifle...and let's not get into big ticket stuff like tanks, planes, and ships. NATO has standardized a lot over the last 60 years, but that's taken a herculean effort - and is honored more in the breach than in the observance when it comes to procurement. (Procedures and other, smaller stuff? Or tactics? There you actually get a decent amount of standardization.)
I've personally thought the UFP makes the most sense, given comms lag and other factors, if Big Starfleet is like federal forces in the US, with planetary defense forces being like the National Guard - they may use the same uniforms, same equipment, same training, same procedures, but the quality of personnel (especially at senior levels) can vary significantly. 10 gets you 1000 that while the line folks may be just as motivated and competent as their UFP counterparts, the senior officers (especially flag officers/general officers) are probably...not even close. In the real world, while I'd never count out the average National Guardsman, patronage and sometimes blatant nepotism and other corruption is not uncommon for the Adjutant Generals and other senior NG folks. And it shows.
Keep in mind - it sounds like most "accessions" (entry of personnel into the force) occur via SF Academy on Earth. And the other locations are probably Earth-like. So you really need to be able to take Earth's climate to train for the Fleet - if you have your own quarters, okay, that's your problem, but the reality is that after 4 years on Earth, you might just have gotten used to Terran-standard climate.
