Welcome to the forum kikomar.
First there seems to be some confusion. Are the bottles you have
Royal Oak Select Rum or
Angostura 1824 Rum? Both have numbers on the label but they are very different rums. Angostura 1824 began to be bottled in the late '90s or early 21st century. Royal Oak Select, on the other hand, has been the flagship of Angostura for many years. If the label is 12 yr. old Angostura Royal Oak 1824 rum, you have something special which hasn't been bottled for at least 15 years.
1) Aged rum doesn't improve in the bottle, though you might find some improvement, if you don't like the harshness of freshly bottled rum, in freshly bottled rum.
2) I'd drink that rum straight, then decide if you would rather drink it mixed with something that will improve the taste.
3) I have watched the label numbers on Royal Oak Select for years and don't believe they mean a lot but you might be lucky and get some information from Angostura, but I wouldn't hold my breath.
4) Your bottles are rum don't have much value beyond the retail value since that rum is still being bottled and is available in several markets.
Over the years, I've tasted a couple of different blends in the 1824 bottle, the latter being better than the first blend I tasted.