Socks - help?

OK, I'm trying to knit Matt some socks. Obviously Matt is a MAN. So I can't exactly follow the pattern as I have been as he is bigger than women, which seem to be who sock patterns are written for.

I roughly worked out how many stitches to cast on and merrily did so... only to find that when I had done a round of 2x2 ribbing that I had a problem. I finishedwith 2 knit stitches. But of course, I STARTED with 2 K st too... which would mean I had a wide strip in my ribbing. Bah. I cast on 70st, so I'm trying to think of some kind of rule. half of 70 is 25, which is odd. If I had cast on 72 or 68 st, half of those numbers is odd. So do I just need to stick to a number which when divided by 2 is even for the ribbing to work? ETA: Aber has pointed out the blindingly obvious. Both the fact that I was clearly searching for the fact that the stitches need to be divisible by 4, and that 2x2 rib is just a pattern repeat over 4 stitches... so CLEARLY you need a number divisble by 4. Doh!

I'm going to rip and be good and do a swatch. I got the harmony dpn set for my birthday today so have a nice range of sock needles finally. Before I only had a 2.25mm set, so was knitting every thing on those. I realised today that all my patterns (and the Opal yarn) are all written for 2.5mm so tis not really surprising that my jaywalkers are too tight is it?!

So other than the making sure my cast on number results in an even number when divided by two, does anyone have any tips for deciding how many to cast on? I measured Matt's leg at the point where the socks he was wearing came to, and it was 23 cm. Just in case that helps! The Yarn Harlot seems to suggest casting on about an inch-worth's less than the required size so they don't fall down. So that would mean making it 20.5cm I guess...

I'd like to try short row heels again rather than doing a heel flap. Are there any good web tutorials? The first socks I did were SR heels, but they were badly written and put me off. Since then I've done the heel flap and picked up the stitches, which is fine, but I hate picking up stitches....