[Renato1 (Renato)]

The highest useful power I've ever gotten in suburban Melbourne from an 8" is 400X a few times, 300X fairly frequently, 200X most of the time. For the very high power, the atmosphere has to be good, and it should be at the time of year when you neighbours aren't running airconditioners or heaters, which will tend to stuff up the seeing.

Basically, if your image is sharp at 200X, bump it up and see if the image is improved. If it is, bump it up again. When it looks like mush, lower the power.

Using a planisphere. Look at your watch and find the time. On the planisphere, set that time against today's date. Go outside with a low power torch. Face South. Hold the planisphere over your head, with the south part of the planisphere pointing south. As you look at it with your torch, starting off with the Southern Cross, you can match up all the over head stars. Face north and do the same thing.

After a while, you stop putting the planisphere over your head, because you don't need to.

Finders are meant to be crisp. On most of them, you unscrew the front collar a bit, then rotate the objective element back or forth until you get the image sharp, then screw the front collar back in again to lock that focus position into place.

I don't know enough about your dob to offer any comment on your last point. But you do have a set up, that should keep you happy for years.

Hope this helps,
Renato