Hi jody - great questions! Regarding crush 2014, only Mother Nature knows for sure! You'd be safe to plan your visit during September through first half of October to catch all the harvest and crush activities.
Napa Valley wineries and hotels are subject to ADA accessibility compliance, and I don't think you'll run into many 'scofflaws' in the valley, so plan your visit assuming you'll have no access issues. If you have doubts or questions about a specific winery, best to inquire with the hospitality director.
The Napa Valley Vintners website is handy for learning about each individual winery in a single website:
As far as motorized tours at the wineries (e.g. ATV, golf cart, tram), I can think of a couple off the top: Benzinger Family Winery and Gundlach-Bundschu Winery in Sonoma both offer an educational tram/4WD tour through the vineyards. Somerston Vineyards in Napa Valley offers an ATV tour through their property as well.
There are probably more, and I hope other posters will add to this thread.
Another idea would be to take the Wine Train: