A bit of a long story but I have a few questions for everyone regarding this situation.

I was recently travelling on BA RUH-LHR-IAH in Club World. I purchased the ticket using 70k AA miles + $726 taxes. Flight from RUH to LHR took off without issue. After landing in LHR I get a text that my flight from LHR to IAH has been cancelled due to operational constraints and I have been rebooked later in the day via PHL on BA and AA but downgraded to economy. Flight from LHR to PHL took off late due to a cabin crew member being sick causing me to miss connect in PHL. BA automatically rebooked me on a UA flight for the next morning, also in economy, before I even landed in PHL.

In PHL I find that one of my bags didn't make it to PHL. I take the bag that arrived and head to the airport hotel. Next morning I checkin for the UA flight but my bag is over 50lbs since I packed according to business class allowances of 32kgs so I pay $200 in overweight bag fees. Eventually I get to IAH.

I had a few questions:

1) Do I apply for the UK261 cancellation and downgrade at the same time? I left LHR 4 hours after the original scheduled flight and arrived at my final destination 20 hours after the original scheduled flight.
2) Do I file the claims through BA's feedback portal which has the option to make a claim for flight cancellations? Or is email a better option? I realize that this will probably all lead up to a CEDR filing months from now but what is the best way to start the process?
3) It was 70k AA miles from RUH but LHR to IAH would have been 57.5k miles so do I make a claim for 75% of the cash price of 57.5k AA miles plus the amount of tax that I would have been charged if I had booked a direct LHR to IAH business class ticket? Or do I need to figure out a prorated amount based on 70k miles?
4) Do I make a claim for the hotel charges, food charges, and overweight bag fees as part of the same claim for cancellation and downgrade or is that a separate issue? I have all the receipts.
5) Am I entiled to refund from AA on the points difference between business and economy on the LHR to IAH leg?
6) What compensation am I entitled to if BA can't locate my other bag?

Thanks