I see no "special" regulations for Marion in the reg book. So, the Zone regs apply. Yes, 2 brookies and 2 bows IS a daily limit. Some peeps misinterpret the "2 daily limits in possession" rule, and think that it is legal to keep 10 fish in one day. It is NOT legal to do that.
I even recently asked 3 different ODFW game enforcement officers this question. And they said it is indeed ILLEGA,L to keep more than 5 trout per day. A person cannot even keep 5 from one body of water, and then travel to another body of water to continue to catch trout. Once you have 5 trout in one day, you must put your rod away and stop fishing.
When I went to Marion in 2000, there was a complete ban on any and all fires.As you will be in a wilderness area; there is no reason to think that the ban has been lifted. So for cooking, you will need to pack in cook stoves of some type. There were about a dozen of us there that trip. We all drank filtered water with no ill effects.