Welcome to the forum, you will find it a great source for all things Omega and watches in general.
Regarding your question, that’s a difficult one, I was on the reserve list for the first ST and my name reached the top of the list last December so I got mine before some of the original reservations, it can happen but it is down to chance. From the original ST thread it appears that payment requests varied depending on where you live, in the UK I don’t think any prepayment was required but in my case there was only about a month between being offered the watch and picking it up.
Your final point really depends on how much you want the ST2 over the CK2998. Personally I’d go for the CK2998 which is a very nice watch and a definite whereas the ST2 is down to chance.
Just one further point if you’re considering when funds might be available for your purchases, Omega say August for the start of deliveries, that is very unlikely on past performance. The ST1 was launched in January last year and I don’t believe deliveries began until the autumn, the same with the 57 triogly which kept going back and back.
Hope this is some help (or confuses you even more!).
Once again welcome.