what Dave said, with a few more details thrown in:
(You didnt specify a budget so...)
1. Roamio plus/pro. (Only difference is storage space between the models*)
2. Mini for 2nd location
3. Slingbox connected to the Roamio's component outputs
-6 tuners - one cablecard (only one saves you a few $$/month... 1st card is free with many Comcast packages.. but this is Comcast, so your mileage WILL vary)
-Multi-room viewing to mini. One shared list of recordings/easily manage recordings/season passes/etc from either room.
-Use either Moca (built-in, puts ethernet onto coax) or ethernet + coax to connect the Roamio n Mini
-You can use the tivo Ipad app to slickly manage your tivo(s) from on the road. Android app has most of the same features but is less slick.
-Roamio can Stream/download from Roamio to Ipad/Iphone (currently has to be wifi on the other end). Android and maybe? other platforms at some point with built-in streaming/downloading feature**
-Continue to Sling from the Roamio, just like you were before.
-Depending on where you are, some Comcast areas allow on-demand streaming on Tivo (basically via an app)
If you need more storage or tuners, swap in a full-blown unit of your choice for the mini. You'd only lose the unified playlist and have to pay for another cablecard.
*Drop-in drive upgrades up to 3gb can make the Plus more cost efficient than the Pro depending on the deal you get, if you can turn a screwdriver.
**Streaming is relatively new, compared to Slingbox which is naturally more mature