With that said, it is a very old house and I am nervous about the potential for future problems/improvements (e.g. the windows are all wood framed single pane, the house is surrounded by trees resulting a lot of moss and debris).What are your guy's thoughts?

Also needs back door replaced and some widow panes are broken in the detached garage. 

There should be two types of goals - stretch goals and strain goals.

It's not like your flipping the property and your strained for time.

I'm about 90% sure its a dual pane window but I can't tell in the pictures.

From what I learned I think I am going cheap filters all the way to not strain the fan. 

I'm flipping a house and my cointractor just informed me that my electrical panel is 60 amp and does not have a main breaker.

Breaking a small window pane to gain access might be cheaper.  

Also, what you describe with the electrical panel is also a pretty major repair, no way VA/fha loan goes through with that so again, the financing contingency should kick in and the deal dies and you get your EMD back.    

I do most of my own plumbing and electrical except for major stuff like installing a main panel.  I