Small update here!
Changed to GeographyUnit.Meters, and CurrentExtent to (-2000000.0, 9045984.0, 3545984.0, 3500000.0) and it made the map show up! Thank you for all your support!
Although, it is very slow, but I will test more of their servers.
Will continue to update.
If I enable TileCache, I get the error "This key does not exist in the dictionary" where the tiles are supposed to load for all tiles.
I noticed that the TileSnappingMode is not a valid parameter here, as found within WmsOverlay.
It is also extremely slow to load tiles. It takes up to 20-30 seconds to load a screen with tiles, and it can take up to 10 seconds before a single tile has loaded. What might seem like an error message that I receive is that the amount of threads increase by alot during map load. As much as 200 at the time.
"hill climbing, change max number of threads 157"
I tested the same map, with the same internet connection within QGIS, and the tiles here seemed to appear within normal loading time.