Walls and Ceilings - Replace windows w/ sliders on Cement Block home

I'm wondering about replacing a wall of windows with two sliding glass doors and am wondering how involved it might be because the house (built in 1950) has a cement block exterior and was built on a slab. Would it be about a day or two day job with experience contractors? Would I be able to get an estimate from Home Depot or Lowes and would that be the way to go ortoo big a job for their contractors and would I save and get a better job done going with a private contractor?

I had Home Depot replace two front doors once and it took two guys a full day to do both. This however would require cutting intoand removing cement block exterior that is underneath the current windows.

If you aren't going to do it yourself, use a private contractor. However, before you do any of it, consider how much block has to be removed & what type of headers are needed to maintain support. Also, would there be heat loss in the winter?