A Hopper has three satellite tuners that are shared between DVR recording and viewing live on the Hopper and Joeys.
A second Hopper adds 3 tuners as well as more DVR storage. Many people on this site strongly recommend a second Hopper with as few as 3 TVs in the house to avoid tuner conflicts. Depending on your viewing habits a single Hopper may be sufficient. Keep in mind that playing programs from the DVR does not involve a tuner.
With 2 Hoppers, the DVR duties (and program storage) are split between the two Hoppers. Timers in both Hoppers must be managed separately and you need to keep track of which programs are recorded on each Hopper. The other limitation is one Hopper can not use the tuners from the other Hopper. So if one Hopper has all tuners in use for recording, that Hopper can't watch anything live even if tuners are available in the other Hopper.
Joeys have no tuners or DVR storage. They "attach" to one of the Hoppers to access its tuners or DVR recordings.
Prime Time Any Time (PTAT) uses one tuner to record "the big 4" (ABC, CBS, NBC and Fox) during "prime time" each night. With PTAT enabled, you have two tuners for watching other live programs. This same mechanism also provides all 4 networks for live viewing at other times even with PTAT disabled. Depending on your viewing and recording patterns, PTAT could be a benefit by providing you with more recorded programs to view later or allow viewing the big 4 channels at several TVs and only use one tuner. While PTAT is recording, there are only two other tuners available for watching other channels on all your TVs. So if you watch little big 4 programming, PTAT could needlessly tie up a tuner.
The Sling adapter has access to only the tuners and DVR programs in the Hopper it is attached to. A new version of Hopper that includes Sling is slated to replace the existing version in the next few days. It too has this limitation. If you want Sling access to all programming/tuners in a 2 Hopper system, you need two Sling adapters or both need to be the new "Hopper with Sling" versions.
Transfer to an EHD is limited to the Hopper the disk is attached to so if you want EHD archive for all DVR material, you need one for each Hopper.
Another possibility is sharing an output from a Hopper or Joey between two TVs. HDMI splitters can feed the same programming to two HDTVs. Hopper also has analog component outputs that could feed a second HDTV. Both TVs view the same program however.
The first Hopper is included with programming. Each additional Hopper or Joey is $7/mo. The DVR fee is $10/mo (compared to $7/mo for other receivers -- up from $6/mo as of 17 Jan, 2013). Expect to pay more for up front for a second Hopper. I don't think Joeys have an up front cost at least for 3 or less. Dish pushes 1 Hopper/2 Joey systems. Special arrangements need to be made to get a 2 Hopper/1 Joey system but it can be done.
