I'm a DIYer and just built a house, doing my own plumbing.

I didn't lube the compression hardware, but then again I didn't read the angle stop instructions and/or maybe I didn't know any better! Any way, they don't leak.

Re: "Should I leave some extra pipe in case I make a mistake and have to cut off the ferrule?" - Not a bad idea, I did it, just in case. And, hold the body of the valve with a good wrench to keep it from rotating, that helped while tightening the ferrule nut.

I would discourage the use of compression fittings. They are the weakest type to use in that application. Typically used by only the wham-bam homebuilders, as they are quick and easy for illegal immigrant faux-plumbers to install.

A family member bought a fairly upscale (built mid-90s) townhouse which was plumbed with compression fitted supply stops. When the time came for a DIY swap out of some toilet tank guts, the valve spun right off the pipe! This created quite the flood while he scrambled downstairs, out the door, and fumbled around in the bushes--in the dark, nach--for the main shutoff.

As an alternative, I'd suggest sweating on a male (MIPS) nipple, then wrapping it in teflon tape and torqueing on a FIPS-fitted supply stop. A nipple is a single, simple joint to sweat solder, even with limited torch skills (as contrasted with a tee, for instance). Plus you can look right inside the nipple and see if there's a silver ring of solder completely around the perimeter of the pipe-end, which is a good indication of a properly "filled" joint.

I see at least 2 problems with that DIY site:

1) Teflon tape or dope on the end of the pipe? WTH? This shows a lack of understanding of how the pipe deforms and seals to the ferrule, and how the ferrule seals to the funneled housing. Tape could possibly interfere with that. Just let the carefully formulated metals do their metal-on-metal thing. Plus the metal-on-metal squeaking becomes a good indicator of having tightened enough, and discourages OVER-tightening.

2) As pointed out by Formula1, it's VERY important that you use a 2nd wrench to apply COUNTER-torque to the valve body (which has wrench flats for just that), such that the pipe itself experiences close to zero torsion. Failing to do that could collapse the pipe itself, or even compromise the ell-joint inside the wall!

Well, in this case the lines were PEX with copper stubs, so sweating was out. Anyway, I cleaned off the copper really well and installed the compression fittings with two wrenches.

I tightened only 1/2 turn further after full hand tightening. They haven't been tested yet, so the jury's still out.

Yes, I also saw that crazy reference to using teflon tape. "WTH", indeed.

I have sweated on angle stop valves onto copper stubs connected to pex lines. I just wrapped a wet rag around the stub close to the wall and then did my soldering. The pex was unharmed.

Sure, but the guy in charge of the project said "no sweating".

Not much room to wrap the pipe anyway. Can only "see" about 1/2" of copper when assembled w/ the escutcheons, which are plastic.