the only one of your questions I would hazard a guess at would be the spit-like substance ringing the stem on your lavender...could be spittlebugs, which whip up secretions into a protective blob of foam. Pull one apart gently and you should find a light-green little fellow there in the middle of it all. I never have a problem with them but the stuff I have growing are mostly natives that are used to spittlebugs taking an occasionaly sip out of their stems. It is possible that they might transmit certain diseases I guess, but that is something someone with more knowledge can tell you about. If you aren't sure, just spray them wioth a good stream of water and that should wash them off.

Ok, I will hazard a guess at the others but I am pretty sure I am way off...never seen variegated solomon's seal, and the red stem is odd, but that is probably because all the SS I am familiar with are locallly growing and not nursery stock. There is probably a bi-color variety so you could be close on that one.
The other reminds me of a weed called cleaver that starts out looking a bit like that, though the leaves are narrower in cleaver.

Like I said, the only one I feel comfortable with is the spit-looking query. Maybe someone else can add to this.

Dirtgirl's guess is correct. It is variegated solomon's seal.

The last picture looks to be Galium odoratum or it's wild relaltive, G. aparine - but it I don't think of that as having a lemony smell. Does it get white flowers?

I also would guess spittle bug on the lavender but.......