Just saw that model 3 reserved in my account. Any idea of the meaning of 9-digit order number?
Yes. It is a 9 digit order number.
There use to be a sequence number for reservations so you knew where you were in the line for MS and MX but this was removed a while ago. When you get the car depends on a number of factors but Tesla owners, location and top of the line models ordered get priority in the past. Do not disclose your RN#.