Poplar is dirt cheap, while maple is fairly expensive. Neither takes stain very well as others have said. You might look at a moderately priced wood which will split the difference. Birch is an option, but I have a feeling your cabinet maker may not like it. Alder is another wood that takes stain well and has a similar look to maple. Your cabinet guy will probably be fine with it, since it's currently pretty popular for furniture and cabinets and reasonably priced. Here's a photo of my den in alder. I did the staining and finishing myself so I do have some first-hand knowledge on working with alder (these were RTA unfinished cabs). It is entirely possible to get good results with stain on maple - I made a coffee table with maple legs and alder top that matches the den perfectly. But I think the issue here is that two different people are making the poplar paneling vs the maple shelves, so your odds of mis-matched colors are pretty high.

One Shot Lettering Enamel is an oil based paint that is typically used in signmaking shops and pinstriping cars. It used to be lead based, but has been changed in the last few years. There are still some lead based colors out there but the Black and White are non-lead based. Sign painters use this product because they only get one shot at lettering a sign. I believe that it will work indoors as well. All colors are premixed in the factory and are individually priced, the highest being metallic gold which is about $60 a quart. The basic Black and White start at around $23 a quart. It does seem to be durable product. Works great on Doors. It is manufactured by SprayLat and comes in about 45 colors. The colors are very vibrant and don't seem to fade very much.

Who makes these bonding primers? Is that different from just a primer? Cover Stain, 123, what are those brands? Sorry but I am clueless...used to buying "oops" paint and not going for best quality (yes, my bad...now it's time to grow up methinks!) Thanks for your advice!

You WILL see minute cracks where the rails and stiles meet on an all wood door, as well as where the panel is inserted into those stiles and rails. That's just how wood behaves in the presence of moisture--including your wood floors. They too will gap in the winter and potentially cup in the summer. It can be controlled a bit more if you use AC in the summer and use a humidifier in the winter, but nothing on the planet will stop it. Choosing wood stiles and rails with MDF panel will stop most of the cracking at the joint where the panel meets the stiles and rails, but it won't stop the cracking where the stiles meet the rails. If the natural expansion and contraction of wood will drive you crazy then don't get wood. Get an all MDF door that is routed to resemble a recessed panel door or raised panel door or whatever you are looking at. And then choose thermofoil if you want a "perfect" paint job too. Because even sprayed MDF will still not be 100% perfect. It's about as good as you get for smooth paint, but thermofoil is smoother and more even still.