I would think that you will want to use a wider door casing as well. In my opinion the narrow MODERN door casing will look out of place with the wider CLASSIC base board. You should be able to simply remove the casing from the pre-hung door and replace it with your choice..
I have never worked with the foam crown molding, but I would have no problem using it.

Agree with the wider door/window trim looking better. Also, ceiling height makes a difference, especially with crown. 8' ceilings only need narrow crown and/or base/door/window trim.

Plastic crown is fine as long as it is painted. Otherwise, any joints will show as will nail holes. Some plastic crown is glued in place---especially when no joints are needed in a straight run.

One issue with foam molding that I've seen is that if it gets a hit, while solid wood molding might get a little dent, the foam will have a giant dent. Further, the wood is somewhat easily repaired using a number of standard methods, not so with the foam.

An inexpensive way to get a hefty base board is to use 1"x6" boards and a 1 3/8" base cap. It will be nearly 7" tall and it's an easy install. I would use a 1x 3/4" base shoe with that but that's a matter of taste.

The base board provides the visual foundation for the room. As such, it's the one piece of molding that can be out sized compared to the rest. Get some of the material you intend to use and lean it against the wall in your room and see if the size works.

If you feel that your existing case should be larger a backband is an inexpensive way to add some size. You'll need a table saw for this but if you have one or can get to one it's easy after that. Take some 1"x6" and cut it into strips 1/8" wider than your case is tall. Sand the banding and break the leading edge with sand paper. Install it around the outside of your exisitng casing. When it's finished you'll gain 3/4" in width and extra depth. Visually it will appear even larger.

I've never used foam crown but it could work. The trim in commercial buildings is commonly glued on foam. Once it's painted who's to know or care? They used to make it out of plaster even cement and nobody cares. I can't imagine how your crown molding is going to get dented. If you try it report back on how ti went; I'd like to know.

I went with 5+ inch baseboard with quarter round and the wider door trim. After looking around, I only had two door trims to change (from prehung doors) and decided that it was worth it.

Have not purchased the crown yet, but received a sample from this company and am very pleased with its quality.

To shop our online store click this link: www.creativecrown.com/store/
For more detailed information about our molding click this link: www.foamcrownmolding.com/
Thank you for all your help and suggestions

Here is a link that might be useful: Creative Crown

I've made the mistake of using two different sized casing, one different on the door and another around the base. I'm not crazy about it. Go the extra mile and do it right. same sized all the way around.

Styro crown moulding is not so bad. You'll probably paint it and no one will know the difference. I think a good professional job could be done. Go and see what is in the market. Perhaps just some pine made the way you would want it to be. When it comes to crown moulding you can realy stack up a mighty pretty one.

good Luck