Hey there. Sounds like a good plan. The answer is, of course, to get both.
I don't have the DA 50mm f1.8, because I have a Pentax M 50mm f1.7 manual lens. But if they are optically similar, its a great deal. And f1.8 can be very useful in low light situations or portraits.
I have the DA 35mm f2.4, and.. I dont know. Sometimes I get amazing sharp photos with beautiful colour (especially for landscapes), sometimes I do something wrong and its not that great. I use it a lot more since I bought the K-01. Affordable, sharp, wide angle, fast AF, compact. Only problem is that it has a little distortion, so its not perfect for close up portraits.
I have the DA 40mm XS, too. Its a great lens. Very sharp! Very fast AF, very compact. I like its bokeh, and the rounded aperture blades make sure it stays nice at all apertures. Virtually no distortion. Works for almost anything, portraits, landscapes, architecture photos.. Only problem with the XS is the 27mm filter thread and lack of QS (then again, the 35mm and 50mm also don't have QS), so it might be worthwhile to think about a used DA 40mm limited (you get QS, distance scales, sensible filter threads, and lens hood).
I can easily recommend the 40mm XS. The 35mm, too, but I tend to use the 40mm more (I find it to be more consistent in quality). I kind of tell the lenses apart in terms of purple/green. The DA 35mm is great at rendering green colours. The 40mm XS renders more purple. Or maybe its just me.
And remember that on APS-C, 40mm is not wide. I would go for 50mm only for the extra brightness of f1.8 and if I didn't already have a dirt-cheap, but amazing 50mm lens.