In your state the current building codes require an insulation value of R30 in the attic for new home construction.
- That is between 9-11" of insulation depending on the product used.
- I would insulate to at least these levels.
However before any insulation is installed, the attic should be air sealed to prevent air infiltration into the home. Review an article I wrote on air sealing here.
Ideally once you have air sealed and insulated your attic there should be no reason to go up there -- looking for leaks as you said. It is not recommended to store stuff in the attic as it sees extreme temperatures and stores this energy, making it take longer to either heat up or cool down.
Now if access is really needed, an elevated platform can be built by installing 2x framing perpendicular to the existing joists. Then when the insulation is installed plywood can be installed for flooring.
For more information:
Read "We are wondering if it is safe for us to follow the energy experts' recommendation of blown in cellulose insulation in our attic." a Q&A answered by Lucas Johnson.