Whole Wheat - Creating pieces

I've been plugging away at my Whole Wheat cardigan when I get the chance, so far I've finished all of the back piece and am about an inch off finishing the left front. Isn't it looking fantastic!? And oh so soft!

I tried being a 'good little knitter' and read through the pattern before I started, but I couldn't make head nor tail of it. However I'm happy to report that as I'm getting to each piece it's making sense (so far!)

I'm also trying to decide how long to make the sleeves - the pattern has short sleeves, but I don't think I'd get much use out of a cardigan with sleeves that long, so am considering trying to work out how to modify the pattern to make the sleeves longer - but the question is, how long?!