Don't know about vinyl siding hanging stuff, but I do know how to hang a really heavy weight mirror. In fact, my DH is in the process of hanging one inside our Cape up in Massachusetts now. It takes two boards, one mounted on the wall and one mounted on the back of the mirror. The long edge of the wall-mounted board is sliced at an angle to allow the mirror-mounted board to mate with it, and thus spread out the load across the width of the board. If I can draw it out for you with keyboard strokes, I'd do it. ]__\ is the basic shape. The slanted angle is on a long edge of the board. I'd make it a 2" thick board at least. The two boards come together so that the edges are like this \\ .....Hope that shows you. With your mirror, a second row of wood near the bottom might secure it against any wind trying to twist it. But basically, this will hold up a LOT of weight.

That huge tree should be looked at by a pro to see if it is a risk. I would remove the two bushes at the entrance. They look uninviting and act like a visual gate saying "Keep out!" Extend those two beds so they curve on up the sidewalk toward the porch for a more welcoming look. Have a landscape architect plan the installation for something interesting and/or blooming all year round. I'd remove anything growing near the house foundation that doesn't bloom. Light, airy and more loose plantings will be more friendly and appealing. For the porch, I think it would be more interesting to re-work the door area. I can't tell what the trim piece above it is, but the lights are too small. I would get a door with glass that repeats the design of the other windows and paint it white so you can keep the storm door. If you want to remove the railing, replace it with low planter boxes sitting on the porch floor. Fill them with seasonal annuals and/or greenery at different times of the year. If you keep the railing, add planters to them. If you sit out there, some space between the boxes could be bench seats that look like the planter boxes.

The entry is impressive, and the doors take up most of the width so I’d skip the planters. Maybe a large, flat piece of metal sculpture on the wall to the left of the door. Lighting looks perfect to me. Add a large impressive welcome mat.

I think these might be pretty on your bench. https://www.target.com/p/2pk-18-5-gilford-outdoor-throw-pillow-festival-blue-pillow-perfect/-/A-54358579 Then you could add a coordinating mosaic table. https://www.kirklands.com/product/Outdoor/Outdoor-Furniture/Outdoor-Tables/Colorful-Mosaic-Outdoor-Side-Table/pc/3011/c/3012/sc/3014/226427.uts