I've had good luck with ski-sleds that just had the skis bolted to the
sled with wood-slat back-up so bolts wouldn't pull thru the plastic. I
didn't try to keep the camber in the ski as is pictured at the one
link---it seems like the load will eventually bend over the bolts.
Well, we use our ski-sleds for ADULT sledding as well as for pulling
stuff around! We find that the plastic sled bends with the camber of
the ski anyway.

I vaguely recall 9.5" being a good comfy ski track width (when I built
a track-setter). There was a thread here years ago on the variations---
I don't recall the standard. If you're off by an inch it feels
awkward!

We connected our poles just with simple rope loops---never had
failure.

I always GREATLY prefer shock-absorbing poles. And the poles are
always CROSSED for good turning.

I made my poles with a dowel, eye-hook, hollow alum conduit that the
dowel could slide inside of, bungee cord. It worked great for classic
striding, for skating, for shoeing. (I agree that shoeing could use
shorter poles for tight terrain.) I remember doing some fun adjusting
of pole-length and bungee length to keep skis from hitting the sled
and to absorb my entire ski-lunges.

With any kind of heavy load a suspended pole is needed otherwise you
have a wretched sense of starting/stopping all that momentum no matter
what your mode of travel. Maybe there's a place for a rigid pole,
though.

Have fun!

I'll do a photo write-up on this at my OYB site sometime. My pulk is
presently disassembled so I can't provide pics right now.

--JP
outyourbackdoor.com