1. Largely depends on your preferences but vinyl is tough to beat from a performance to budget standpoint.

2. Unless there is some sort of trim detail between the two, they ar likely mulled as one unit. The sill can be replaced without necessitating a full tear out.

3. Yes. New construction will mean new interior trim.

4. Tough to say. See what your impressions of the contractor are and look at work samples.

new construction means all new trim on insude and out.
usualy a contractr who offers a higher quality vinyl window brand will more than lokely do a better job opposed to a contractor usingg the cheaper brands.
higher quality brands are Sunrise, Okna / himark, gorell, and soft lite.

lower quality brands are pella vinyl, andersen vinyl, american craftsman, silverline, and MI Windows.. obviously many others.
and yes, both pella and andersen make a low quality vinyl.

New construction actually means "new construction". This is when the house is framed and sheathed, and the windows are mounted in rough openings with 'installation fins' or 'nailing fins', prior to the siding being applied. If your talking about replacing windows in your house, and if you use new construction designed windows, you'll most likely spend a lot of money on a lot of extra work involving alterations of opening sizes, siding, and fitment issues.

I am merely correcting your terminology. If you live in an existing house and are replacing the windows, you will want to use replacement windows because they are accurately custom sized to the existing openings. They will be installed either as inserts or as complete tear-out "full frames". The insert and full-frame will be the same window, just different installation methods. The full frame will replace everything back to the studs, including interior and exterior moldings. The full frame may have a modified jamb to receive sub-jambs, or full frame may be inserts that are sub-jambed in the same way, but with the standard jamb.

An insert will be installed in the existing frame, preserving existing moldings. Or it may be installed in a sheetrock return opening either on top of the sheetrock, or to the studs with a sheetrock cut-back.

With both methods, the outside trim can be wrapped with colored sheet aluminum custom bent to fit for a maintenance free exterior. High performance vinyl will most times cut down your glass area unless you do a full tear-out and re-trim.

Hope this makes sense to you. I thought it might help you as you talk with window companies, contractors, to use correct terminology so they understand what you're talking about.

Hope this helps.

when i said interior and exterior trim, i obviously meant going down to the studs. you can also order windows with an extension jamb.

Sorry, mmarsel, I was mostly addressing the OP as per the title of the thread. Didn't mean to make it sound like I was correcting you.