Newbie want hints on vented box and drivers

I've been reading a lot of formulas to calculate the correct volume for a vented box, but there seems to be more solutions than there is drivers out there. Could someone tell me how to choose the correct formula/charts?

In the end maybe I don't need a vent for my box? I'm making rear speakers for my home theater and I've singled out two drivers I wish to use:
* Seas 19TAF/D as tweeter
* Seas ER15RLY as mid-bass

Anyone have a comment on my selection? Seas because they're 'local', and respected as good quality, even if I select rather cheap drivers.

If I get this right, I'll make a subwoofer and maybe new front speakers as well.

The reason for asking about vented box is that the EBP for the driver is calculated to 107, witch should be suited for a vented design.

Would the sound suffer noticeably if I made it a sealed box, considering this is rear speakers and there will be a subwoofer and front speakers with bigger drivers?

Hope someone has time to help a newbie. :)