The first thing I would do is see how the mobile home is supported. Is it on a foundation that will hold the weight that you plan on adding?
I have installed windows and vinyl siding over the aluminum vertical siding on a mobile home before. However, I did not use insulation.
If I were you, I would draw up a plan so that every piece of this job fits right.
What you are going to want to remember is, how you want the windows to look after this job is done.
You currently, probably, have about a 2 1/2" window jam and I would add a wooden casing around the outside of the window that is thick enough to look right after you but up to it with insulation and then adding the siding over it. (Probably a 2 X 4).
You will also have to figure that you will be adding drywall to the inside so, this will effect the depth as well.
Depending on if you want window sills or if you plan on picture framing the interior trim, will decide on what windows you should buy.
A standard window with a 3 1/4" jam or a narrowline window with a 2 1/2" jam or something else.
So, 1. check the foundation, 2. determine the final wall thickness, 3. decide on interior trim appearance, 4. select the windows that will meet your needs.