My husband has psoriasis and psoriatic arthritis (what every dude in his twenties wants!). We've spent years experimenting on him. One thing that we've learned is what helps one person might not do anything for someone else with the same diagnosis, so buckle up because you've got a lot of experimenting ahead of you.
First thing that jumps out is the sneezing congestion after alcohol...that could very well be a sign of histamine intolerance. It's an easy thing to google to find some symptoms and ways to experiment with dietary things to see if that's the case.
Rather than telling you all the things we tried that didn't work, the one thing that DOES work is getting sun (a tanning bed works, too). However, even taking high dosed of Vitamin D for months did nothing for him, but getting direct sunlight in the areas where he is prone to getting some psoriasis works everytime. Now that it's winter, his psoriasis is a little worse, and he really needs to be using a tanning bed regularly.
From my research and our brainstorming and Sherlock Holmes work, his psoriasis doesn't seem to be affected by any foods in particular (we've done years of painstaking elimination diets), but we are convinced that it is somehow related to digestion. My husband has issues with this; he's not intolerant of any specific foods, but he has some IBS tendencies and low stomach acid...and likely a leaky gut. I've read that leaky gut problems are often involved in many autoimmune disorders, especially psoriasis. Does your husband have any digestive issues that you know about (symptoms like gassiness from either end, acid reflux, etc...)
Also, how his is sleep? The body views lack of good quality sleep as a stressor, and over time this kind of chronic stress can lead to autoimmune problems, like psoriasis. We've figured out that the major culprit for my husband is sleep; completely unrelated to what he's eating, if he's not been sleeping well for a period of time, he gets flares, but when his sleep is better, his autoimmune stuff quiets down.
If you can share some more info, I could try to give more detailed suggestions, but in a nutshell, I would suggest:
1) Sunlight/tanning bed time
2) Focus on good digestion, which should include plenty of probiotics, not too much fiber, bone broth, and L-Glutamine (an amino acid that the body uses to repair leaky gut issues, among other things)
3) Good sleep, reduced stress, and general relaxation