i have birch with MDF panels. Mine are painted. So far, they look great although its only been less than a month. I know, its not long enough. But, my bathrooms and the cabinets in my living room are poplar with MDF centers and are now 12 years old now. they have held up beautifully. I don't know why most cabinet makers here use wood for the boxes and outer door frames but use the MDF centers. It works though. I have absolutely no seperation showing in the cracks where my panels are. I do see this in some of my crown molding where the pieces were joined. maybe that could be the advantage of the MDF panels? By the way, I don't know if I would have gone with solid MDF for the boxes and door and drawer frames. It is particle board and I'm not sure how well they would hold up structurally over time.

1) Panels that are half to 2/3 the thickness of the frame are par for the course. It's not a hard and fast rule, though, because you need to consider the width of the frame members as well as their thickness. Rails and stiles that are 1" thick and 1" wide would meet your criteria but wouldn't work well. I imagine this is fairly obvious, but I'm just making sure. 2) The size of the gap needed is proportionate to the width of the panel. 1/8" is probably fine for most kitchen cabinet doors. Especially wide doors and/or unstable woods could require more. Remember that you only need that gap along the edge-grain sides of the panel . Where the panel's end grain butts into the groove, no such gap is required(again, I don't know what you already know). If you want to get into the math, pick up Bruce Hoadley's Understanding Wood. By consulting various charts and formulas in that book, you can learn that the moisture content of film-finished, kiln-dried wood kept indoors in most of the U.S. varies within a range of about 8% over the year. My guess is that that presumes very dry air in the winter (no humidifier) and humid in the summer (no central air). Obviously YMMV. Anyhow, the book has charts of average tangential and radial shrinkage of various species, and this information can be used to calculate the amount of movement you need to allow for. Yellow poplar is listed at 8.2% tangential (flatsawn), 4.6% radial (quartersawn). Imagine a panel in yellow poplar, 18" wide. We'll say it's rift sawn, and use 6.4% as the shrinkage number. Over a MC change of 8%, our hypothetical panel would grow (or shrink) by about 0.33". In other words, an 18" wide poplar panel built into a door with only 1/8" gap per side in the driest part of the year could conceivably grow enough to bottom out in the slot and push the frame apart six months later. 3) I'd say 50 degrees is borderline, but workable. The basement shop can be a bigger problem in the summertime, because the coolness (in the absence of air conditioning) raises the relative humidity; summer humidity is high to begin with, so a shop environment that raises it further is problematic. In the winter, however, humidity is likely to be on the low side, so you've got some breathing room to tolerate the cooler environment. Below 50 degrees, however, many glues and finishes don't work so well. --Jon

The horrible smells were more likely from the finish on the PB piece than the materials it was made of. But that's just a guess. I have painted shaker cabs with wood center panels. My painter put caulking around the inner side of the rails and stiles (all around the interior panel) to alleviate the stress on the paint. So far so good. The cabinet boxes will be made of plywood- which will have lots of glue in it. If you're sensitive, that could be a problem. They do make plywood that uses non-formaldahyde glues. One is called PureBond. It ain't cheap, but ya' gotta do what ya' gotta do. BTW congrats on the impeding arrival!

I don't know anything about these cabinets, but my answer should bump up your question and someone else might answer it more directly. I would think that if the cabinet box is made from plywood the doors would also be made of plywood. However, all of the sellers you list have either phone numbers or live chat methods of contact. Ask your questions directly to them.