Crafting is capped just as harshly as spellcasting. You can't craft an item with a higher CL requirement than your own CL.
Just a nitpick, but Artificers can craft at +2 CL. That opens up a whole new level of spells.
I don't think so. In E6, 4th+ level spells simply don't exist. Spell lists for full casters end at 3rd level. Your Artificer could craft items that list CL 7 or 8 as prereq though, if no actual 4th level spell was called for.
Actually, they do. Our current E6 game has us hunting down monsters for the SLAs to craft with. You just can't learn them as spells.
Emulating them with UMD however...