One thing about identifying plants is that once you get a handbook and then go find them yourself they're a lot easier to remember, so I wouldn't fret much about that.

As far as medicinal plants, I'm sure there are a handful that are common and easy to identify, so you learn those and point them out as you go along and you look like Euell Gibbons out there to everyone without a clue (the target market).

Some are easy, like mint, echinacea, goldenrod, birch, etc. If someone asks about a certain plant that you can't ID from memory be honest, tell them you have no idea, but have the handbook ready to help and get the client involved with the process of identifying them. That's fun for all.

I've guided a few hikes here. One was for a bunch of plant nerds that work with the Conservation Dept. That was a thrill for me, they knew practically every plant down to the specific variety, and you should have seen how excited they got when they found one that none of them could identify. We didn't make it a more than a mile from the trailhead, when we got to a glade area they all got stuck. There was just too much cool stuff for them to want to go any further. I walk right by it every day.

I heard more latin being spoken that day than all the rest of my days combined. It was total overload. They told me the names of hundreds of plants and I don't remember one of them.

Guiding hikes is a pretty cool job. Most of the people you'll be with are happy to be there, and eager to learn. The only advice I can really give is to keep on eye on all of them to see how they're holding up, and stop for a rest whenever you see someone struggling a bit. Don't ask them if they want to stop, just tell the group to stop for a bit. If you can spot a plant you're familiar with talk about that, or tell a story, and when everyone is rested move on.

If they wrote you, I'm sure the job is yours if you want it. I'd jump on it, you never know where it will lead you.