Aye eye to that...
It's a serious challenge bringing it all together on a successful level. I'm on number... oh hell lost count, and still am not entirely sure what my little efficiency drop came from in a 2-3 day period.
The most difficult aspects in building this thing:
The proximity of key components physically on the board (MOSFET, input caps, output caps, totem pole)
Getting ESR as low as possible
And last but DEFINITELY not least, the %&$#ing coil.
The hardest part about the whole project. The inductor makes this whole thing a Pandora's box from hell.
Other things that come to mind...
Heavy traces for the current path, particularly the output side amongst the output caps, since you will be dealing with higher current there than on the input side. Don't skimp on the input either, but it's not AS important as the output.
Caps, caps, and more caps.
Keep a FUSE on it during development, and after if you're going to go above 50W or so. You'll be dealing with some 'fake panelling' for some of your early test runs, and current can get away from you QUICKLY!
In addition to a fuse, use BALLAST RESISTORS! I have a string of 3 8R 20W Dale ceramics that I use for this. They will save you a lot of time and trouble in things like replacement MOSFETs, and also provide you a controlled way of estimating your real world (actual panels) gains. They are not perfect replacements for panels, because the 'curve' is linear rather than a wonky hyperbola, but you'll get close enough to say whether its ready for the panels or not.
Get all your guess work out on the bench, because unless you have a completely clear day with at least a few hour stretch, you'll learn all about frustration as even the thinnest clouds come and go, screwing with your head. The 'fake panels' won't do that, and any discrepancies will have to be with the circuit itself.
Be prepared to let the smoke (and fire if you do it just right) out of a half dozen MOSFETs before you get a handle on things. Granted, I didn't have as much trouble with the buck as I did trying to get the forwarder going (dead count was like 20 before I gave up), but I still had some problems along the way.
One day I'll master the forwarder too, just because I refuse to concede that a bunch of parts on a board can out-wit a human.
TTFN
Steve