DC you sound like you are rather anxious and that's not really surprising given the life-changing (and wonderful) news you've had. You also sound like the sort of chap who likes to have everything sorted out well in advance and also who likes to have everything clear and on the table.
You feel like your integrity will be compromised by telling lies or half-truths to your employer, but it doesn't have to be this way. Your employer has no right to ask what is wrong with you if you have time off for a medical appointment or two, even if in your office you are all very open about these things normally. Just tell them that you (or your wife) have a medical appointment (both true) and don't say what it's for. If they do ask (which they're not meant to do) then you can just say "I'd rather not say", which you are perfectly entitled to do. If you'd just found a lump in one of your testicles are wanted to get it checked out but felt you were being a bit silly and worrying for nothing, would you want the whole office to know? I'm not trivialising testicular cancer or pregnancy here, but you do have a right to keep personal health information private.
The weeks between now and the end of the first trimester will not last forever, and if you get through those with a healthy, viable pregnancy then you will be able to tell work, family and friends, and they will not hold it against you for keeping it a secret until 12 weeks, as this is totally normal. You will have plenty of time to plan and read up on birth and parenting and the very different times ahead.
Your wife will also have another 27 weeks of being pregnant and everyone knowing about it, at which point, as other posters have said, an awful lot of those people will only think of her pregnancy and not her. For this reason I'm glad that we haven't told many people yet, although I'm dying to shout from the rooftops that I'm pregnant, I'm quite pleased that we've still got a few weeks of sharing this little secret because it feels to special, and also that people are still treating me normally, as me.
You mention that your boss has never met your wife and won't until the Christmas party, but have you considered how awkward it could be if (and I hope this doesn't happen) she miscarried and then gets to meet a man who she never knew before but knows she was pregnant and miscarried. Whether your wife knows he knew or not. I'm not saying you're being thoughtless, just that you probably didn't think of that because all this is so new to you.
Also, with telling family, you do need to be careful and agreed on who you are going to tell and when. I have friends who told siblings in confidence about an early pregnancy and were horrified when those siblings told others the news. Your family may be the best secret keepers in the world, but there is always a risk.
Lastly, it must be difficult for your wife not being able to talk to her mother at this time, and it's great that you see that. My mother and DH are my two rocks, but there is something very special about the different conversations I have with each about my pregnancy. It is also making me grieve once again for my dead father, and how I have missed telling him my happy news. Your wife needs you to be that one and only rock right now, and that may feel like a heavy load for you at times, but I am sure you are able to support each other for a few weeks,by which time she may feel like telling a few people (especially if you have an early scan, which I recommend if you are both a bit anxious), but clearly you will agree this together.
Congratulations on your wife's pregnancy and I hope you both get to relax and enjoy it soon. It sounds as though you are already starting to get your head around some of the many enormous thoughts there are to consider.
Best of luck