Wow! Great!!

I'm not a professional but I'll offer my humble opinion.
One target at the same time, unless they are related (eg a 'movie' in your head). Before you fall to sleep may work well...

Some things may happen even with few visualisations - depends on any limiting beliefs or attachments you might have.
If you wish something a lot you can do it more often, maybe even until fulfillment.
Some people just send off the wish to the Universe and trust fulfillment will happen.... Or remember it now and then... Trusting that it will happen is the main thing.. Having a good feeling about it..

Maybe you could just replace any negative films in your head with positive/good?
Just a question - if it is something you enjoy and wish, why would you want to stop?

Your questions made me think, and realize that maybe I've given up on some things too soon too! (Because I was lucky to not have to visualize some others much!)

Good luck!!