I suppose I am biased, but if its your gun, do whatever you want to it. Don't listen to other people who say oh no, it will kill the value if you reblue it. If its yours and you don't buy guns just to sell them, then do what you want.
Now onto the question at hand. Cold blue is meant as a touch up when you screw up a hot blue job, not as a full finish. I know its expensive, but if your like me and want your guns to be in good shape for your children, grandchildren, etc., then have it professionally done.
The polish is the labor intensive part, as the blueing itself mainly consists of knowing how long to leave it in each tank. If you want a matte finish, get it bead blasted. If you want it slightly glossy, but still not blindingly so, get a 400 grit polish, If you want a mirror finish (and I don't know why anyone would, but like I said before, they are your guns), get a matchless finish.
Some people will advertise a 320 grit finish, but I think its not worth the difference between it and a beadblasted finish.
As for myself, I like my hunting guns beadblasted and blued. No glare, and I find it to be durable.
I have not yet tried this, but I have heard people parkerizing their guns and then having a finish applied over the top of it (i.e. robar, duracoat, etc.)
I know this was a long convoluted answer with information you probably didn't ask for, but I hope it helped.