The only things you need Permission for are 1) missions, or 2) things that would noticeably alter the PPC. As long as you're not doing those things, you're free to write whatever you like. {= )
As for the questions:
1. I'd personally prefer it if you adopted him permanently, but since Jay and Acacia did say he was free to use, I don't think there's anything stopping anyone who wants to borrow him (though it is polite to ask the Board first). If that is what you decide to do, just make sure you address what happened to Agent Robyn, who he got partnered with.
However, that said, I agree with the people who are confused that you don't want to make your own character. If you don't have a team ready yet, why not just wait until you do? Heck, I hung around for almost four years before Ilraen came along and I partnered him with Nume. {= P I'm an extreme case, but still. There's no reason to rush into writing missions if you're not satisfied with your team.
2. DoSAT tends to appropriate canon technology and modify it for PPC use rather than make stuff up out of whole cloth. The CADs, portal generators, and disguise generators are a few exceptions. Also, as someone else said, what's wrong with a regular leash?
3. No one's ever really bothered about this before, as I recall. I am positive that HQ does not do any translation of its own accord, though. I am also positive that every agent is equipped with a Universal Translator as a matter of course, just like they're equipped with a flash patch, a CAD, and a remote activator; and it would have to translate written words as well as spoken. The agents couldn't do their job without it.
However, as others have pointed out, the Rule of Funny trumps just about everything. If you need the UT to stop working for a joke, then it will.
As for what it looks like... well, no one's ever bothered about it before. I figure it would have to be something very small, not easily noticed. Maybe it's even built into the flash patch. They've already got a microchip and SEP field generator in there; no reason for the UT not to be part of the same device. ... Of course, in that case it wouldn't work if the agent wasn't wearing the flash patch.
Then again, there is more than one kind of Universal Translator in the multiverse. The most obvious is the Star Trek device by the same name. But then, Douglas Adams gave us the Babelfish; Farscape offers translator microbes; some species have the ability to learn languages very quickly and/or communicate on a different level entirely and don't need one at all; and then there're all the various types of magical translation spells and/or artifacts you could wish for. I wouldn't be surprised if the PPC makes use of all the options available.
~Neshomeh