The limit switch prevents you from hitting the glass plate unless you knock it wildly out of allighment. and it homes on Z at a relitivly slow rate to prevent accidental damage even if you did. Is it possible to hit and crack the plate? Yes. But i’ve only ever heard of that happening once or twice with non lulzbot machines.
The machine itself will ship pre dialed in and ready to go after assembly. assuming you don’t knock it around too much while putting it together it should be level from the start. Avoid turning the Z endstop target when you are putting it together in particular. If you do have to allign it, then yes, the process you outline will work, with one tiny additional variable. You want to do that allignment with the machine at full printing temperature, because the nozle itself expands slightly when heated. The 2.1 nozzles are less prone to that than the older ones, but it’s still something you want to account for. To that end, you may want to use a thin metal rular as the feel gauge rather than flammible paper.
After you print something, in an ideal world you would remove the filliament and place it in an air tight dessicant filled box to ensure no humidity permiates the plastic. In reality almost everyone just leaves it on the machine unless you plan on not printing for a while.
The ABS and PLA in the same extruder being a problem is due to the different melting points of ABS and PLA. After you print something there is usually a bit of plastic left inside the nozzle. if you start with ABS, which melts at 230c, and then go down to PLA, which melts at what, 160c? any remaining ABS in the nozzle will act as a plug and cause you major issues. You can overheat the PLA to ABS temperatures, which will cause the PLA to burn but probably clear the ABS plug and eventually after a bunch of wasted PLA be able to print. Going from PLA to ABS, you just end up burning out the remnants basically at ABS temperatures.
It’s just easier to stick with one type of plastic
A flexystruder will work with ABS, the ABS will just wear down the liner faster than the flexible stuff, You can get a 1 foot long section of replacement liner from Mcmaster carr for about $0.50 cents, so it’s not a huge problem.
One thing you will run into when you start swapping out extruder and hot end assemblies, is that not all hobbed bolts are dimensionally identical. The lulzbot ones are closer than most, but even there i’ve found that the correct extruder firmware setting for one hobbed bolt tends to be slightly over or under for the next unless you take extra care and order a pile of extra hobbed bolts and match them all using calipers. Easy enough to work around using the filliament width setting in slic3r, but somethign to be aware of.
I’d start with the ABS plastic personally. thats what I started with. PLA seems like it would be easier because of the lower temperature, but some of the properties of the material itself make it more dfficult to work with. PLA can expand slightly under heat and can lock itself into the bore of the hot end unless you have a fan on the hot end itself. It also transfers heat an unbelievable amount back up the unmelted filliament, which can cause problems on slower prints. A fan is usually the fix for that as well.ABS can be a bit more difficult to get to stick to the bed at first, but once you have that part down, I find it easier to work with ABS,