Welcome to Flyertalk and welcome to the BA forum Kaimik, you have definitely come to the right place to find out more, and I hope you will continue to participate here.

You can get seat allocated for free 72 hours before departure, so it's only worth paying if you want a very specific seating arrangement or location.

My general take on flying economy is that the nature of the cabin is that you best go the cheapest way. The economy products will be broadly the same, so to my mind cash is king; and the differences at premium economy level fairly small, maybe BA will have the better catering, Delta the more modern seats. A key issue is whether you are in the Super J version of a 747, which is a good bit of kit, and definitely worth trying while we still have the amazing 747s around. Looking at the Route Tracker on thebasource.com you have a good chance of getting a Super J, these have 86 seats in business. The seats and IFE are quite good on that version, the mid J version with 52 seats in business - well that's complex but overall best avoid due to the older seats and IFE.

Route Tracker | The BA Source

One other option to consider, though this is for the summer months: starting from Vancouver so you can use the A380, which is superb in all classes. Also have a look at going to Aberdeen, Edinburgh, Glasgow, simply because so many more airlines go there, and there is just more competition. It's easy to get to INV from all of these locations.