Moving back to Cable TV. New Setup...

So I am destined to be moving over to Charter TV(from which I already get internet and phone) here in CT, due to large cost savings($125/mo for a least a year with their triple play). I currently have Directv and their costs have just gotten too high for me.

With Directv I currently have 3 HD DVR's and a Genie(4 TVs) which gives me multi-room viewing as well as 11 tuners to record with, that are viewable on all TVs. I know Charter's current DVR are pretty bad and they don't have multi-room viewing either, so I suspect I will be frustrated with them very quickly.

So enter Tivo Roamio. I was going to start with a Roamio Plus first and then add pieces along the way, eventually getting to this...

Roamio Plus on main TV
Roamio Standard on Living Room TV
2 Minis, one in each bedroom.

In thinking of costs, I doubt I will go lifetime on either of the Roamios, so over all, I think this setup would be a little cheaper(minus upfront costs) vs the current costs of 4 Charter DVRs per month...

4 Charter DVR's @ $6.99/mo each = $27.96/mo
DVR Base fee = $10.00/mo
Total = $37.00/mo

Roamio Plus = $14.99/mo
Roamio (Standard) = $12.99/mo
2 Minis = $ 0.00/mo
2 CableCARDS @ $2/mo each = $ 4.00/mo
Total = $31.98/mo

I "think" I am calculating this right, but I am not sure if using a cable card requires me to still have the base "DVR" $10/mo service.

My other questions are...

Should I get the initial Tivo Roamio Plus before or after the Charter TV install, since after may allow me to go to the office and choose my CableCARD and TA vs having an installer show up with a particular brand(I hear Cisco ones may only allow for 4 of the 6 tuners to work)?

Also, I have never been a Tivo subscriber before(I did use the old Tivo Directv receivers back in the day) so would this change any of the costs with Tivo?

Thanks