Hi folks, I'm hoping this is the correct place to post.

I'm BA Blue, so no status of any value at all. I have two itineraries coming up in a few months. I'm flying in Y on both.

First flight is a solo RFS redemption from MAN-ORD via LHR. I'm travelling over the Chicago Marathon weekend, out on the Thursday during the day and back on the Monday overnight. I'm being offered the chance to pay for seats now or wait until check-in. There's still plenty of space available when I look at the seat map, in both directions, but I'm conscious that it could be a busy flight nearer the time.

Much as I enjoy looking out of the window while the plane is taxi-ing and taking off/landing, I'm not sure I'll get the benefit from a window for the whole 8 and a bit hours, I won't sleep during the day so I'll just chillax with a beer and a movie, so I'm thinking I'd prefer to get myself a seat on the aisle, preferably on the outside of the middle three. Am I best off just sitting on it and keeping checking nearer the time? Do prices go up? Also, if I wait until check-in, can I check n and book my seats 24 hours before the first departing flight, the one that gets me from MAN-LHR, or will I have to wait until 24 hours before LHR-ORD to check in and select my seat?

Second itinerary is a cash booking with my family, LHR-CAI. We're 2 adults, a 12yo and a 6yo. I'm conscious that the 6yo will be put next to one of us, but ideally, on the 3-3 seating configuration, I'd like to have both kids with one parent on the same set of 3, while the other parent could reasonably be elsewhere on the plane. Again we're flying in Y. Would it work if I paid just for the two kids, say, seats A and C, and then they'd have to put one of the adults in the middle? Or is there no need to worry about booking at all?

I don't want to pay unnecessarily, and I don't want to use Avios, as I'm saving them to hopefully take me to New York in 2023.