Op, I realise this may be too late, but we've been away.
First do not worry about your lumps and bumps – I doubt he'll worry too much!
I suggest you start by sending him upstairs to get the bed ready, get his clothes off, lie in whatever position you need him in. Your'e in control.
Give him waiting time, and be fully clothed when you blindfold and tie him. Tie and tease. Be soft, be hard, you do have nails. Cup his balls in your hand and see how much he can take. Those dangly bits can take a lot more than is realised.
Following on from Guilty, whisper in his ear, I'm getting changed. Make sure he can hear.
Lots of whispering in his ear as things progress, suffering/pain before pleasure, etc.
Use two hands on his erection as if you were using a pepper pot.
You'll be nervous at the start, so will he, use your imagination and enjoy the journey. I'm sure it'll be worth it.
Oh, if he makes too much noise, stuff your knickers in his mouth! Good luck.