General selection and installation questions

Finding some time to install replacement vinyl windows and siding in the next couple months, still have a few things I'm not sure about. My home is circa 1965 with the original drafty old aluminum framed single panes. Lower level is brick while upper story is currently Masonite siding.

1. Is it likely all current frames have nailing fins and if so, how would this be addressed when removing the old frames from the brick faced walls?
2. The upper story window frames display at least a 1/2" reveal beyond the current Masonite siding. Firstly, since I plan to replace the siding in conjunction with these windows should I choose new construction? Secondly, if not, what would be the proper way to determine the offset of the window to gain the correct amount of reveal? Should it be calculated based on the chosen siding dimensions?
3. I saw a fleeting mention of replacement windows which did not require removal of the old aluminum frames, interestingly I even recall it mentioning that style as being a version of replacement window gaining popularity. To me it just doesn't seem right but have to wonder (depending on what the replies are to #1 above) whether it might possibly be a more appropriate choice.
4. A simple one...What's the consensus...aluminum or fiberglass for screening?

Looks like all my windows have 3/4" wood jams, guess it's good to know as many retailers could possibly assume 1/2" drywall if I simply measured jam to jam and let them decide my needs. I'm sure I'll have additional questions but for now I've attached a few pictures to accompany the above queries. Any additional suggestion are most welcomed.

Regards,
Ej

Click to enlarge

1. Yes, pry them out.
2. New construction with fins and possibly jchannel and brickmold.
3. Usually a commercial high rise application, jumping the frame or panning.
4. I prefer alum.

Much appreciate the reply Anthony! Great answers, and concise to boot.

At first I was leery of "wrecking" the frame out worried about compromising any weather barrier but now realize all sealing is actually accomplished frame to brick (veneer) not frame to sheathing as will be done on the upper story where there is siding. I did see the commercially available tool and the one made by someone on this forum. If the current frames to be removed turn out to be not so crowbar-friendly I'll cobble together one of my own for the job.

An additional question -- I just realized the window frame is set in the brick veneer opening by about 1/2". When measuring for these windows I expect ordering measurements should be taken at the brick veneer and not the rough opening? Veneer and jam measurements are almost exactly the same at 70 3/4" x 35" while the rough opening is 72 1/2" x 36 1/2".

Yes, I will be measuring rough opening for the sheathed/sided openings that will receive new construction windows.

Regards,
Ej

Your thoughts on measuring are correct.

Thanks again Anthony.

I'm convinced pre-purchase measuring is the most-likely-to-be-bungled process of window replacements. My carpentry abilities were never a concern, now I have confidence the measuring will also be a non-issue.

Best Regards,
Ej