Don't let the high BMI freak you out; my BMI was 36 at booking but managed to have regular scan/bloods done without a hitch at my 12 week appointment. OK, I needed to shift and roll around a bit for the sonographer to get the right angle (at one point I had to stand up and jump up and down to get baby to move!) but we got there.
Having a full bladder does help, but it's a fine balance between drinking enough for the scan and not having to have a pee 2 mins beforehand...
The only thing you will notice is that the quality of any scan photos you get won't be as clear and 'crisp' as some others because of the extra layers of fat they need to get through to get the images. Was still more than happy with mine though! 
My 20wk scan was also fine. Despite my BMI we got to see an incredible level of detail this time.
I've also been referred for a consultant appointment in June, however the midwife has reassured me that it's purely a precautionary measure and she's absolutely confident (because I've had such a straightforward pregnancy thus far, touch wood!) that the consultant will say that I'm fine to continue under MW led care.
You may find that, later on down the line, you need to do a glucose tolerance test for gestational diabetes. I'm looking on this as a positive thing because a) it's better that they catch it sooner rather than later rather than go through pregnancy with it undiagnosed so you can get the medical support you need (has happened to two people I know as they weren't in 'high risk' categories to start with so it wasn't picked up until v. late) and b) if you do have GD you get extra growth scans to make sure you're not having a humungobaby, so you get to peek in and wave at your baby more often than anyone else does before the birth! 