First up should be addressing MagicJack. I'm not a fan, but you should also be aware that they have models now that don't run off a USB connection and software with your desktop:
http://www.amazon.com/dp/B0061R1XI4Personally, if you must be absolutely cheap with your VoIP service, I think there's better options as well with
NetTalk.
As for Google Voice at home, if you really want to do four GV numbers with Obi hardware, you're going to need either the Obi202 or two Obi1xx units. That said, you can forward multiple Google Voice accounts to the same non-GV phone number so long as it's listed as a "home" number with Google, and not a "mobile" or "work" line. However, people dialing out will have to choose their own GV line first for caller-id unless one of your four GV numbers wants to be known as the "home" number for everyone.
Finally, regarding handsets... if you're wanting
true GV integration with a phone, you're going to need to go with an Android handset at minimum, otherwise all you can hope for is push-email notifications of incoming messages and a dedicated app for callback and SMS replies, or using Google's mobile interface through the web browser, and yes, WiFi would be necessary if you're trying to minimize data usage on the mobile plan. Personally, that'd be great for some folks, but a non-starter for others. If you're going Page Plus for Verizon reception, I can't really think of any specific models of feature phone that aren't likely going to be ESN blacklisted due to being former Verizon Prepaid handsets. If you go Android and Page Plus, TheDude recently namechecked the
HTC Incredible as being really cheap aftermarket currently (well under $100), and as an added bonus, officially supports
CyanogenMod if you're into that sort of thing. If you choose to go with a GSM provider like
P'tel for the wife and kids since you're buying new handsets anyway, the
LG Optimus One is a relatively decent priced GSM Android workhorse and supports
CM as well. Beyond that, let me
link an article I recently posted not for the content entirely, but the assortment of research links for alternate GSM handsets to an iPhone that are WiFi enabled and can do roundabout GV support without being Android handsets.
That should get you started.