iMac Purchace Decisions

I have major considerations in a new purchase of a new iMac.
i5 i3
RAM 4 or 8?
21 or 27″
Love the 21 with the specs of the 27 SSD and Hard drive together.
Then it’s also due for a revision. After the new MacBook Pros last month, you’d expect that the iMac will get Thunderbolt the latest data port that will be “it” for years to come I need to know that it will have longevity.
The configuration?  according to the rumor, Wednesday morning, will tell what configurations are available.