Not sure which Yaris to pick - Avant
I know you have a 1.0 at present but are you sure you wouldn't prefer the 1.3? It's a good lively engine and uses little extra petrol than the 1.0 as you have to work the 1.0 hard to make reasonable progress.

With regard to options I think the T3 is worth it over the T2, the T Spirit not worth it over the T3.

You'd get a better price selling your car privately - but then you have the hassle factor. Have a look on Autotrader and see what equivalent cars are going for: they tell you whether it's a trade or private sale in each case.