Jeroen,
I have about as many hours in my logbook flying in the mountains as you.
From your postings I gather that yours is further a bit thinner than mine and a lot of others on these shores.
There is absolutely nothing wrong with that or the wish to go and have a good time and at the same time expanding one's experience envelope.
I do have to share with you though that the combination of things that you are willing to undertake seems pretty ambitious and that I am concerned that you are overstretching yourself a bit.
So that is of my chest.
On a different note I think that there may well be something wrong with your take off calculations as for my Maule with the 235hp Lycoming the take off would require 1450ft in no wind conditions at Big Bear with an ambient temperature of 60degrees F. It is generally well accepted that a Maule has a better take off profile than a Cherokee and would be surprised if you would only 300ft more than the Maule.
Go and fly with an experienced instructor over there and have fun, make sure it does not end in tears. Those mountains have propensities that flatlanders like you and me know very little about.
Frank