HELP-Salt Lake City Flagstone

I have three flagstone walkways on my property, and I'm wanting to find someone to extend the size of one of them (the dog runs over the existing grass until it is mud--I'd rather have nice clean stone!). As well, there's a staircase made of red flagstone connecting the driveway to the back walkway. This winter I've noticed gaps around the stairs: it looks like chunks of concrete have come loose or have come out. In addition, I've found a spot where a good-sized flat sheet of stone (maybe 5" by 12") has come right up off the surface of the front walk. The property is in Salt Lake City; I'm sure the extreme cold and wet are the major causes of damage. The house was built in 1938, and I think the flagstone is from that era. I have adjusted the "tilt" on a couple of the walkway stones myself, so I know what's underneath is Rocky Mountain soil (except where I added sand).

QUESTIONS:

Whom can I rely on to extend the one walkway at a reasonable price? I'd like to keep this as simple as possible

whom can I rely on to repair the gaps appearing around the stairs? do i need an engineer or architecht? the stairs come around a circular brick planter, and I've noted that that they subtley slant toward the inside of the spiral--I assume this is so water will run down on that side. I'd like to avoid screwing up the overall basic idea

what can I do to protect the stone from absorbing water and freezing in winter? I love the look of the natural stone, and I'd like to preserve it if possible. (I'm careful about using only minimal amounts of ice-melt in the winter, and use only the kind that's safe for paws, but I'm sure the winters are hard on these walks.)

thanks too much