I sold a 361 for $450 and traded my other 361 for what I would like to think was at least another $450 ( a 028 WB that used to be mine anyways and an MS 460, was what I traded for it). So $400 is more than fair. Heck, on FeeBay, yyou ain't gonna find one under $400!!
I run an 18" 3/8 semi-chisel on my 026 and really love it. I tried the 18" .325 (ok), and 16" and 20" 3/8. My saw handled the 16" 3/8 fine, but seemed to bog down a little with a 20". I split the difference and put a new Stihl 18" on it, the perfect compromise!
Gotcha. I have no experience running a 346 in a professional situation. My 260 was always very reliable.