The tubes you're going to buy for the DIY stuff are probably glass tubes, which behave differently than the tubes Universal uses. Rodney is correct... high wattage gives you gobs of cutting power, but you'll have a hard time turning it down for engraving.
Looks like the biggest I can easily fit is a RECI 100w. Hopefully that's a good compromise on cutting power and flexibility.
Features? Rock solid drive train is #1. Smooth, no slop, and quick.
Heh, that's big on my list too. I'm using linear rails which are major overkill for this application but they work great and will give me years of perfect movement.
Some sort of motorized bed would be #2
This one is interesting - due to the size of the laser bed, I was planning on using a "pinned" bed system so I can raise and lower the bed accurately. I was then going to have the final focusing mirror be position-able +-1" or so to give me final focus. This was going to be combined with a little focus touch-off-tool so I can find focus super fast. Is the motorized bed that critical? I guess I can't see myself switching material thickness frequently enough for it to be a problem.
and you'll want honeycomb
Interesting. Most of the cutter DIY people are using aluminum lighting grids. Is the honeycomb superior to that considering it's >4x the price?
The other thing I'd say is make it easy to service, especially after a fire. Fire is one of those "when, not if" things.
Good to know - I've designed it with easily removable panels but I'll take extra care to ensure everything is serviceable.

Thanks much for the advice!

-Mike