My PO put glass, flared, front fenders on mine. No side markers. Looked just fine that way. Just this week I installed side markers because the wiring was all there already and I like the way they look with the rest of my package. As above do it before you paint if you can, but mine were already painted. The rectangular hole needed is smaller than the light housing exterior and smaller than the bezel that goes against the body panel. So you will be able to hide the cuts if you paint now, see how it looks, and change your mind later.
I used a 1" hole saw (fiberglass/tile abrasive bit) and then drilled small holes at the 4 corners and finished it off with an air saw. If you measure and take your time you can get it done with just about any tools and then clean up the edges. All of it will be hidden if you cut the smallest hole necessary. Buy and install the screw mounts for the body - the little plugs that the screws mount into. They come with the complete front marker kit if you buy it. Consider clear lense markers if you like that look. I kept mine stock amber.
Where you mount them exactly will depend on your fenders. Mine, being flared, left fewer options than a stock fender.
If you already have rear side markers, are yours vertical or horizontally mounted? Assuming they are horizontally mounted and you intend to do the same up front, measure the drop from the body line and follow the same spacing It's around 4.5"). Spacing back from the front of the fender will be up to you and the shape of your panel. I don't know what stock is, but the rear ones are right up againt the seam. I spaced mine back an inch because I liked it there.