3.5 years later I'm considering this again with today's technologies

my current plans are;
I'm trying to mix the concepts of a sla device with plotter technology

Build a dlp printer with a mobile print head that moves on 4 axis xyz+ focus
The print head is to be a modified dlp projector or tv projection system with a base detail of minimum .1mm

Build area of 20.5cm*23cm*23cm
if I can focus in I can get better resolution, absolute minimum spotsize for 400nm and crappy optics with a numerical aperture of .54 is 770nm .77micron .00077mm or damn small... I remember reading achieving minimum spot size is very difficult, but dropping a zero makes it achievable. .0077mm or a little under 1000'th of a mm at this level of detail the print head is 1mm across I dont think this is achievable with my optics setup.At 100th of a mm resolution the image is 1cm across, this is my goal, but I will consider this project a sucess if I can get a full sheet print area. at .1mm resolution thats 10 pixels per mm or a 2x3 grid of 1024+768 pixels like in the tv I am parting out.

Like a standard SLA machine I will be lowering a platform in resin. the resin I am planning on using is makerjuice which is supposedly VOC free and will float on salt water. I think this is brilliant since the proposed build volume is about 3 gallons or ~400 but I can float a liter on salt water and print for 25$

To maintain a constant surface I think I will try with an overflow pipe attached to the bottom of the build chamber. with the Z platform in the top position I fill the chamber to some mark with super salty water and then add at least enough resin it oveflows from the pipe, then lower the platform to its start position. The salt water overflow should keep the surface of the build tank the same the entire time as the platform supports continue to be lowered in. I'm doing it this way to keep from having to build anything super complex inside of a tank that's under assault from salt water and resin could harden in.

I've ordered too many parts I'm not sure what all I will need I have a Pi and camera on the way to run octoprint with... using the hdmi output of the pi I plan on driving the video of the projector.

It seems from reading in #reprap I might want to use an arduino, the support of users makes problem solving seem easyier the pi is just newer.

I am planning on a variable print resolution as defined by the z axis print head, change size. I see some real challenges to anything involving software more  complex than printing images serially like  an inkjet does.
        I would like (not planning on pursuing yet) for the printhead size to optimize printing. for example back out and print a large area, zoom in and detail, type of thing.