Hi - based on my experiences, however, we are in NWE so not sure if that makes a difference.
1 & 2 - Yeah, the default filter is like all users in your home group and for some groups, that is a lot of people (one of my groups has like 2,000 people). However, if you change the filter to something else, it does remember that filter. So the next time you visit, it should load faster. I try to remember to change it back to a "My Filter" where it just shows me so that it loads faster. (Although, I don't always remember to do that. LOL!)
3 - Now this one confuses. For the Resource Planner, you can share filters with other people for them to see it. The Workload Balancer is the one where you cannot share filters so you have to log in as people to recreate. In Planner, if you hover over the filter, you should see an icon that is an arrow going up and to the right. That is the Share option and allows you to have others have the filter.