The biggest thing if you're working + fulltiming is to make sure you go in with a plan for income. The RVing side of things is the easier side to figure out. I have quite a few friends who went into fulltiming as families with no RVing experience.
When shopping for rigs- try to make a friend or take someone who knows about RVs and trucks. I'd hate to see you get into a lemon of a unit.
Rig size- for just 2 people, you can be as short as 20' and as long as 40'. The longer you go, the less places you'll fit into. Depending on the type of camping you like, that could be a problem. (Or not- we're in a 42' fifth wheel and have been happy with where we can get in. Though, there have been some places we would have liked to stay.)
For costs... they vary greatly. If you boondock a lot, you'll save on nightly fees but you'll have a sizable investment in battery + solar power + backup generator. If you stay in RV parks, you'll have the nightly cost. The longer you stay, the less expensive it is (nightly is the most expensive, then a little cheaper for weekly, and then a lot cheaper for monthly- though then you get into paying separately for electric).
Depending on where you are, Thousand Trails can be a way of saving money. But they come with use restrictions.
What we found, I budget $50/night for RV parks. In the last couple of years, that has ran the gamut from $32/night in 2015, $45/night in 2016 and again in 2017. My goal for 2018 is to be at or below $30/night with a focus on camping club membership use (Thousand Trails, Passport America, and Harvest Hosts) and boondocking. Right now through mid-March, I'm at $18/night in Florida. We'll see how it goes.
But while our housing expenses have gone down (truck, camper, lot rent + utilities), a few other expenses have sky rocketed. I work online and REQUIRE internet service daily from 9-5. Between my cell phones and cellular internet, my bill runs $350/month or so. As well, our fuel costs have jumped significantly because we drive a big truck every where we go. (Not to mention traveling from location to location with our house in tow.)
The other big cost is our exploring/edutainment costs for us and the kids. We eat out regularly because we're constantly in new places and want to try the local fare or we spend money on attractions and touristy things. We offset that some with museum memberships that have reciprocal entry to other places, but it still gets expensive. For instance, Meteor Crater was a roadside stop as we drove from one location to another but we dropped $50 for just a couple of hours of exploring (totally worth it for us, though!).
Lastly, you mentioned satellite internet - it's slow and expensive. It's good for a backup to cellular internet, but I wouldn't rely on it for day to day use. For internet options, THE place to go is:
http://rvmobileinternet.com/