Thanks for presenting this during our Geospatial Cafe! Looks very useful!
I wonder if, to get rid or the haze, smoke and clouds you could try using the Harmonised Landsat and Sentinel-2 imagery instead as this is collected every 2 - 3 days or experiment a bit with the dates of the post-fire image to get rid of the smoke and clouds or perhaps use s2cloudless.
Also noting that it is possible to upload and import your own shapefile to GEE if you already have an Area of Interest (AOI) you want to look at without having to specify the polygon coordinates.
Harmonized Landsat and Sentinel-2 | NASA Earthdata
NASA's Harmonized Landsat and Sentinel-2 (HLS) project generates global land surface reflectance data every 2 to 3 days at 30 meter resolution.
