2. We started using the chase subsystem from the GMG as a retreat system, and made sure to use the version where the opposition advances at a steady rate so running away is always a more appropriate challenge than fighting a higher end creature.
This is quite what I was talking about. People who wonder why flight isn't an option are often making an assumption about its practicality that frequently doesn't sync up with the game mechanical reality; doing what you did here is addressing that.
3. We made it so everyone can sense everyone else's level directly, along with dungeons and such before they set out, everything is balanced for four players of the designated level, with some intentional exceptions. Regardless of the parties actual level or composition, players can adjust their play accordingly when they see that something is higher leveled than they are-- and higher level creatures are generally less aggressive toward lower level PCs because quite frankly, they aren't as much of a threat, which also makes the lower level PCs a bit safer.
The problem here I can see is with things that are, in one fashion or another, predators. The low-hanging fruit is always attractive.
We've been playing this way since late last year and its been working out super well barring some issues with my own depression making upfront prep hard, and recruitment for online community games always being a challenge, it sounds some of us came to some of the same conclusions.
At the very least the discussion in this thread has been pretty rational about it and shows everyone at least moderately understands the mechanical realities of the system.