The throttle trim should be set up so that you have a good idle with the trim in the center. That way, you can adjust it for different weather / altitude / fuel conditions.

It's a bonus if it will kill the engine when brought all the way down (But a very good bonus to have and a target to shoot for)

As far as the Trainer 60 with a 40...

The "Trainer" 60 is really an intermediate trainer (aka "Second Plane") although there's really no reason why it can't be used as a first (Especially when you have a little past experience). But you didn't mention what "40" you put in it.

If it's a good 40BB, it might pull it ok. Take offs could be difficult if you fly off of grass, and you certainly won't be doing much in the way of aerobatics. But if you can get it off the ground, it should at least pull it well enough for you to learn the basics on. Then, when you're ready, you can go to a bigger engine, or a smaller plane.