I would advise AGAINST doing this. For a few reasons;
1. Its your first time. Dont trip on acid for the first time without anyone else tripping, You will be on completely different levels, and nothing that you are interested in will correspond with anything they are interested in while you are tripping and they arent. It will probably lead to a lot of confusion and potentially anxiety.
2. From the sounds of it, your sober friend doesnt sound like he has ever tripped before. This could just be information that you have left out, or not. But I think it is very important that anyone who acts as a sitter for an experience should have experience with that substance so they can know what to expect, and more importantly, if their services are needed , so they know what the heck to do, and more importantly WHAT NOT TO DO. (easiest way for a somewhat difficult trip to turn into a BAD trip, is to have an idiot who has no idea what the user is going through try to interfere.
3. Has anyone here ever tripped at a rolling party? It sucks, Everyone is just like lieing down rubbing eachother, blowin eachother up and trying to talk to everyone about everything that they love etc etc..., but have you seen someone Rolling, while you are not? They look like hideous zombie mutants, imagine that TRIPPING... FOR YOUR FIRST TIME...
Honestly everyone is different, But I would suggest you wait until either you have some friends that want to trip too, or atleast dont trip while your other friends are all rolling, the time of the night when you need their company the most (to interact with them and help ground/integrate the experience) they will all be asleep, and you will just be awake still tripping, with nothing to do, and alone.