1) Lest the delicate porcelain of my loneliness crack
This is the best of your suggestions, in my opinion. I think it is phrased quite nicely, and shows the metaphor clearly.
2) Lest my delicate loneliness porcelain crack
This one is confusing because of the order of loneliness and porcelain. As mentioned in a comment, switching the order makes it okay.
3) Lest my delicate porcelain loneliness crack
When you use attributive nouns, the first noun is the one describing the second. It makes more sense for "porcelain" to describe "loneliness," because that is the intent of the metaphor. In 2), in contrast, it sounds like "loneliness" is describing "porcelain" -- so it comes across like "lonely porcelain," which doesn't make much sense.
4) Lest it crack, the delicate porcelain of my loneliness
Although this would be understood, it feels clunky. It feels like you're going out of your way to move the words out of their natural positions. If you really want "crack" to come first, you could use the transitive version of "crack," but you'd need a subject -- something like,
5) Lest your approach crack the delicate porcelain of my loneliness
Unless you like 5), I think the choice is between 1) and 3). It depends on how you want the poem to flow. The stress pattern of "delicate porcelain loneliness" has a nice kind of sing-songy feel to it, while "the delicate porcelain of my loneliness" sounds a bit more like someone speaking.
*As a comment above noted, lest is used with infinitive verbs (technically the subjunctive mood), so it should be "crack" instead of "cracks" here. That said, when the verb is at the end of the phrase, it's far enough away from "lest" that speakers may not notice it's wrong -- I certainly didn't notice until we moved the verb towards the front, closer to "lest."