Welcome to the Boards TapDancer. How fantastic to spend your 40th birthday at WDW and what a way to celebrate!
I stayed at POR in May and my family is DH, myself and DS10. Because of our family size, we did not get a room in the Aligator Bayou section; we were placed in Magnolia Terrace. Therefore, I did not see the trundle beds.
But when I was booking, I did ask about the trundles and was advised that it would probably be okay for kids under 9 years of age. The beds are double sized beds so I hope your kids like to share!
You did not provide the ages of your kids other than to ask if the trundle was okay for an 11 year old. The answer to your question would depend on whether your 11 year old is the oldest or youngest in the family and whether your 11 yo is on the larger or smaller side of 11.
Unless you wish to look at DVC villas, the alternative to POR is a family room at ASMu, a cabin at WL, taking 2 rooms at a Value or to see if the new resort being built is potentially going to be ready in time. Depending on the age of your kids, you may want to consider the family room at ASMu because (I believe) it has 2 bathrooms.
From memory, basic dining would include 1 TS, 1 CS and 1 snack per night that you are staying, per person. Its currently valued at about $45 per adult per night. The TS and CS meals potentially could include drink and desert. Or you could use the TS for a buffet. To qualify for free dining, you are paying for accommodation at rack rate.
To see whether this would be worth it for your family; or whether you are better off with a % discount off the room, you would need to spend some time investigating the dining menus, which can be found on AllEars. I'm an Obsessive Compulsive Planner, so I tend to start a spreadsheet and choose what I think I would want to eat per meal per day (for me and the family), cost it out in full and then compare it to the
DDP. Remember - there is a lot of food included in the DDP, when you add the desserts. If you don't eat dessert or don't want to sit down and eat at at least one restaurant per day, then it may not be the offer for you.
You'll also need to see if you are going to go to any of the buffets or character meals. I think for me the breakeven point was if I was planning on going to at least 5 meals where I was sitting down for TS, buffet/character meal in a 9 night stay.
In previous years, people on the free dining offer have been able to upgrade to another plan for extra $. Again, you need to work out what the difference is in terms of package and whether the Deluxe plan options is something that you would be using and getting value from a food perspective.
There are a number of accommodation options that are off resort. You would need to check out what is appropriate and then run the numbers, including transport costs e.g., car rental or otherwise; and if renting a car, the parking/entry fee.
Welcome to the world of Disney.Fuzzy.Maths!
For what it's worth, I took the % room discount and bought Quick Service dining. I knew I was only doing 1 character dining and possibly 1 Table service and it worked out better for me. I was also doing a split stay, so I was happy with QS/CS meals for the first half at a Moderate and then moved to a Deluxe and paid for meals OOP.

