Next steps

What are my options in fixing this fender? I’d like to save as much as possible, but I know the reality of rust repair in that you have to cut back to clean metal.

What is the best method of cutting this out? Grinder, sawzall, etc,?

I plan on replacing with new metal, should that be flanged or just butted when welded in?

Any opinions or suggestions are welcomed.

Mechanically inclined, but very green when it comes to bodywork. Thanks!