An artifact that becomes a creature due to Tezzeret’s Touch can’t attack unless you’ve controlled it continuously since your turn began. It doesn’t matter whether or not it was a creature at that time.

A Vehicle enchanted by Tezzeret’s Touch becomes a 5/5 creature. Crewing it won’t change its power and toughness.

An artifact creature enchanted by Tezzeret’s Touch becomes 5/5 instead of its normal power and toughness.

If Tezzeret’s Touch becomes unattached from an artifact that’s attacking or blocking, that artifact will be removed from combat unless it’s normally a creature or another effect such as a crew ability is also making it a creature.

If the enchanted artifact is an Equipment, it becomes unattached and it can’t be attached to anything for as long as it remains a creature.