Before selling off your rolling stock, evaluate which equipment can be converted easily as some items are hard to find in 2-rail. I've converted several cars to 2-rail and new acquisitions since 2009 have been 2-rail. What made conversion easier for me was I got onto a "buddy system" with a couple of 3-rail operators and we routinely make "truck trades" which mutually reduces conversion cost to not much more than the cost of postage.
Locomotives are more difficult. Some you'll have to sell off/replace or have converted. I opted to buy MTH scale-wheeled locomotives back in 2009 and that has worked pretty well for me, even though I run at a 3-rail club. Since I have a large collection of locomotives, the layout I'm building for the house will be hybrid (I bought a pure 2-rail Sunset 44-tonner and also have my eyes on other pure 2-rail locomotives). I'm getting rid of some of the 3-rail units.
