1. The ceremony itself. If I were to be married by her pastor (she has a longer history with her pastor than I do with my priest), would I be permanently excommunicating myself? Is it effectively self-damnation? Permanent "catechumen" status? Eventually able to receive communion?
Your situation is complicated because you are a catechumen. Have you been officially received as one or do you merely consider yourself one?
The ideal is obviously to finish your catechumenate, become Orthodox, go to pre-marital counseling, get married in the Orthodox Church, and proceed with your married life. With prayer and patience, there's a good chance your wife would eventually decide to embrace Orthodoxy. In my experience, this happens in a significant plurality and possibly even majority of "mixed" marriages, especially ones where both husband and wife are believers and a good match.
To return to your questions: If you were already Orthodox, getting married by her pastor would indeed result in your excommunication. Right now, however, you exist in an interstitial state: not fully in or out of the Church. As such, the intent of the law is surely that you act as if you already were Orthodox. But the "letter" is not as clear. So, this is truly a case where only the specific advice of your priest and bishop can offer final clarity.
2. Can I even be married in an Orthodox ceremony as a catechumen?
If not, could I be chrismated sometime after? Or am I barred from receiving communion (like because the marriage is seen as invalid)? (To be fair, while I'm 80-90% sure, there are still a few matters of doctrine which I do not understand, and they tend to be the same sort as prevent her from actively seeking to join as well--Mary stuff, sacramental theology, etc.)
If you weren't a catechumen, you could get married in a Protestant service, then later become a catechumen, then Orthodox, etc. with no problem. Since you have already pledged yourself to the Church, your situation is different. You can't do anything of this magnitude without seeking the specific advice and approval of your priest (and, by extension, bishop). It's theoretically possible they could have you get married as a Protestant before converting; also possible they could say no to that route.
3. If we were to be married by an Orthodox priest, would her pastor be able to play any role, even if only done separately (before or after) from the ceremony?
If you were Orthodox (not just a catechumen), you could marry a baptized, heterodox Christian. Double ceremonies are discouraged or disallowed. The ceremony would need to take place in an Orthodox church according to an Orthodox rite (not at all like the wedding service your bride is familiar with or probably wants). Your fiance's pastor could not participate actively in the ceremony, but, according to the ecumenical guidelines promulgated by the Standing Conference of Canonical Orthodox Bishops in the Americas, the pastor could be invited to give words of exhortation and benediction after the ceremony itself had been completed. These guidelines represent the majority practice in North America, but not every jurisdiction or parish is the same. Ultimately, such examples of oikonomia
are up to each particular bishop. So, you'll have to ask. If you want to read the guidelines, see pages 23 and 24 of the document: http://www.scoba.us/assets/files/guide_for_orthodox.pdf
4. Are even, say, fully-Orthodox marriages, able to be performed outside the church building (like in a forest)? If not, what of those during times of persecution? Or would that be an act of economy that doesn't apply?
No. Marriage ceremonies must take place in an Orthodox church. Exceptions during times of persecution do not produce a rule for today.
5. What are the thoughts about raising kids in a mixed environment, as far as formal prayers and holidays?
It is *very* difficult but possible. When done right, it works and might even lead to the heterodox spouse becoming Orthodox. When done wrong, it is a source of major marital tension and even divorce. Many resources are available here: http://www.goarch.org/archdiocese/departments/marriage/interfaith
If we were somehow a "proper" mixed marriage, could future children receive communion?