1. Type of wood to use??? I'm going to paint them. Poplar??
2. Jointing? The simpler the frame is the better for me, but i'm not sure what would work best for seasonal windows.

Thanks for the input
Joe

Poplar accepts paint well but is a disaster on exterior exposures.
Pine actually works better here. Cypress or redwood wood be a step up from pine with the preference probably going to cypress.

"2. Jointing? The simpler the frame is the better for me, but i'm not sure what would work best for seasonal windows."

Half laps will be more than adequate. Use Titebond III glue.
Wood movement is not usually much of a problem since the cross sections are normally less than 3-4 inches.
You can get various types of weather stripping to make up for variations in the old windows and surfaces.
Resources Conservation Technology has many styles available.
Some for edges, some that go in grooves, etc.

There are multiple ways to make the frames up and cut the required rabbets for the glass.
A relatively low tech method is to build the frames and then use a router to cut the rabbet.
Some hand work will be required to square off the corners.
Prime, install glass (push points are a simple way to hold the glass before putty), putty, allow to set a few weeks, then paint.