The first thing I would do is get the truck to your local truck repair and have them go over the mechanicals. You don't want to find a major overhaul is in your future after you have done all the work to the rig.
To make my 95 FL120 dependable, I replaced every belt & hose, radiator, brakes, alternator and a few other well worn parts. Be sure to check the tire date(s), if they are older than 6 years than junk them.
Since this is your first conversion I would opt for the cheapest conversion plan. You are going to find that if a conversion is really what you want, than there will be a second go at this. You'll also learn alot from this one as well as what you really want and need in a conversion.
If you do turn the truck in to a motorhome than bag the sleeper idea. The kids will enjoy the ride a whole lot better if they are on a couch belted in and watching a movie, than in a dark sleeper with little or no view.
Keep us posted and be sure to include pictures!
2012 Showhauler 28'6" Motorhome on a Columbia w/ 450 Mercedes.