My situation was not exactly the same as yours, but I did have an experience that I think might help you with your question 2. I visited DH once for a weekend when he was still my fiance. I had come from Prague, where I had been working, but I had quit my job so I was unemployed, had no proof of ties to the US or finances or anything (I was only staying 2 days, so the finances probably weren't a big deal, but still). I also didn't have a clue about what to expect from the IO, since I had never been questioned on entering the UK before. When he asked me why I was coming to the UK, I blithely said "To visit my fiance," which he homed in on immediately. He started asking me about why I had been in Prague, for how long, was I sure I was only staying 2 days in the UK because "that's an awfully short time," did I have a date set for the wedding, where would we be getting married, where would we like to settle, etc etc. Fortunately, I had my ticket to the US in my carry-on, but I think what really got me through was the fact that I knew the rules. He asked me, all crafty and trying to catch me out, if I planned to move to the UK immediately after my wedding, and I said "Well, I have to get a visa first, don't I?" After that, his whole demeanor changed, and he just checked my ticket, stamped my passport and sent me off.
So the moral of this rambling tale is that if you can demonstrate that you know the rules and intend to follow them, ie make sure they know that you know that you must have a fiance visa and you must apply for it from the US, then that is a strong statement in your favour.