Congratulations on the bfp neat!
In answer to your questions...
1. The date used to date your pregnancy is the date of the first day of your last period so you would be 5 weeks now. Conception dates aren't used because many people don't know when they conceived, when they ovulated, or what their cycle length is. If there is any doubt about your dates tell your doctor and you can request a dating scan in the next couple of weeks

2. I've lost two pregnancies in first tri myself so I understand your worry. It's very hard and really a personal decision for you and your partner to make...for me I feel like every pregnancy is a new little being in his/her own right, and deserves to be celebrated for however long they are here

3. There's lots of stats on the internet for miscarriage rates...but one statistic that was quoted to me when I was a nervous wreck with my daughter (by an OB) was that once a heartbeat is detected your chance of carrying the baby to term is about 95%. I found that reassuring.
Before a h/b is seen, the miscarriage rate generally is between one in four, and one in six, depending on who you ask.

4. You won't hurt your bub by sucking in your belly, he/she is very well protected right now. Just don't go doing crunches

5. Not everyone gets morning sickness. I have had it with both this pregnancy and my daughter and both times it started six weeks on the nose. That seems to be the common time for it to begin. With the two I lost I had no morning sickness. But in saying that, it's important to remember that MANY women have no m/s and carry perfectly healthy babies. Just doesn't seem to be the case for me!

6. It's hard to hide a pregnancy when you are sick and cranky for weeks on end. I found it easiest to tell the people closest to me as I would need them to know if anything happened. Friends, aquaintances and work colleagues waited until 13 weeks. Again, this is a very personal decision and depends alot on how you feel about everyone knowing your business. There is no right or wrong, just lots of different ways of breaking the news.

Good luck with your pregnancy, and wishing you a happy and healthy nine months!