I would concur with most of what has been said here. I would also suggest trying to shoot some of the guns before you buy.
Where do you live, The shooting community is generally a very welcoming groups and seems always willing to share and let you find what you like.
I live in Minnesota and we have a group that regularly meets to let new shooters try what we have.
I would suggest you stay away from a rossi unless it is all you can afford. I don't know yet if Taurus's management will upgrade the quality of the guns coming out, but for a while Rossi's have been pretty rough.
Don't rule out well cared for used guns either.
The walther P22 is a pretty good gun, alot of fun to play with, but not really the best practice gun compared to some of the other guns out there.
I would get a .22 in the same format as the gun you plan on shooting, that is, revolver .22 if you stick with a revolver SD gun.
There is no reason to make your home defense/plinker a snubbie. They are really best as a carry gun, but if it is just going to reside on your bedside table most of the time, get a gun that is easier to hold, and more controllable in recoil, meaning a bigger package.
If you look around you can find S&W model 10 police turn backs at a local gun shop, This is a pretty good sticky on making sure you are getting a good one.
http://www.thefiringline.com/forums/showthread.php?t=57816
Good .22's are worth more than the savings in ammo. They often allow a great deal more practice per dollar of course, but as well they are much more PC in someplaces to shoot. I don't know where you live, but I live in the exurbs and shooting a .22 in my back yard will never raise a stink, but blasting away with bigger centerfire will get some unwanted attention real fast. .22's seem to be more sensitive to proper use than a centerfire, by that I mean that shooting a .22 very well means you have to do all the things right. it may be just my feelings about this, but if I shoot my .22 well then I know I will shoot my bigger bores well.
Hope this helps.