Louise, this one comes up more than almost anything else in my inbox, so let me answer both halves properly.
There is no medical requirement to take the two week wait off work. Normal activity, including going to work, does not reduce your chance, so this is a question about what you can bear rather than what is safe. In my three rounds I did it both ways and I ended up in gemma's camp: I found being at work easier than being alone with the fortnight, with the exception of the day of transfer and the day of the test, which I would always protect if I could. The one to watch is a job that is physically punishing or where you cannot step away for five minutes when it gets to you. If that is yours, the calculation is different.
On what to tell them, the framing I found useful is that you are choosing who holds the information, not whether to be honest. You can tell one person and not the department. You can tell HR and not your team. You can say "I am having medical treatment that involves a course of hospital appointments over the next few weeks" without ever saying the word IVF, and that sentence is complete and true and nobody is entitled to more. What is worth checking, quietly and early, is whether your employer has a fertility policy, because a surprising number now do, and it tends to sit somewhere unglamorous on the intranet rather than being announced. Time off arrangements for medical appointments vary by employer and by country, so it is worth knowing your own terms before you negotiate. Our guide to fertility treatment and work goes through this in more detail, and the two-week wait covers what the fortnight itself is actually like.
The bit I would gently push back on is the dentist appointments. Not for moral reasons, for stamina reasons: keeping a cover story running takes energy you are going to want for other things. That was true for me by round two.