Pretty good then... took me a while before I used SpDs with my bikes.
Don't worry about speed at start - you will be slower until you get tuned in. Better to learn and enjoy (hopefully).
Quite sensible walking anything that you aren' t sure of. Just say it's a borrowed bike and you're looking after it for the owner!
From experience no-one cares anyway as you are not a 'normal' cyclist (not you personally but anyone that rides these).
To set boom length you should sit in seat and move boom out with your heel on the right pedal at full stretch ahead. You can do this leaning against a wall to push whole boom level using both feet. Keep it middle ring of course as you may not have enough chain. You should add enough chain to make the big ring to big sprocket as that can happen in laidback land.
I'm out on bike today and will be at shop at 5 or maybe 10min after. Get a tea at Pastures next door. I will be there though as I am every weekday. Some days I'm there all day on a weekday if I have someone test riding or have a delivery of bikes.
I do have another job plus assorted paperwork for LB as I quote options and answer queries etc!