You can't do this with layer effects alone because the inside corners have a curved edge. You'd need to draw the inside square edged bevel yourself. It's not impossible, although probably not something you want to do for many letters, but for one letter it's definitely manageable.
Start off by applying the layer effects as you normally would, then . . .
Zoom in and place lots of guides where the bevel edges and corners are (or should be). Create a new layer. Use the Polygon Lasso Tool to recreate each section. Use the Eyedropper Tool i to sample the colour, and fill with Foreground Colour Shift+F5. Repeat until you've fixed all the problem bevels.
This took me less than 10 minutes. You could probably fix the strokes to have sharp corners in the same way.
Another possibility, if you want everything to be rescalable, would be to recreate the entire letter using filled vector shapes - or dispense with Photoshop altogether and recreate it in Adobe Illustrator, which would be the ideal option if this is part of a logo.