Siding replacement is indeed an ideal time to use a flanged window. The only other thing to consider is that typically you will need to replace interior wood work as well (as opposed the replacement/insert style).

+1

Perfect time to do everything if budge allows.

This is the ideal way to replace the homes exteriors.

By interior wood work you just mean the casing and the sill right? Aslo what are the benefits of using a flanged window versus replacement ones? Do the flanged windows cost more? Thank you.

Price wise for a basic window no they do not generally cost more. However the advantage with flanged new construction type windows is the brands and options become much greater ass not every window company makes insert type replacements but they all make new construction type units.