I agree with previous answers that the primary seasoning should be done in an oven. However, to respond to the updated question:
The seventh and eighth point in the above link talk about repeated
seasoning on the gas stove after every use. How viable is that?
I do that a lot. I don't do it after every use, particularly if I've just used the pan for frying or something else involving oil. But if I've had to really scrape the pan to clean it or have used ingredients (e.g., acids) that don't do well with a cast iron finish, I find the technique mentioned to be very helpful in maintaining a smooth non-stick surface. Just put a tiny amount of shortening (better I think) or oil in the pan or on a paper towel, heat the pan, and wipe it around. Wait until it starts smoking, and remove from heat. Be sure to wipe out excess oil with the paper towel. (If you're careful, you can wad up the towel and do this with your hands; if not, use tongs to hold it.)
By doing this technique repeatedly over a couple months, I even was able to restore a pan that had been deeply scraped and scratched with a metal utensil (by a friend who didn't know better) which disrupted the even, non-stick surface.
I've also found that the stovetop technique gradually helps to smooth out the interior pan surface and improve its quality over time. (This is particularly true of newer cast iron pieces that aren't machined smooth like older ones were and have interior pitted surfaces.) Yes, you could do it through repeated baking and seasoning in the oven, but if you're patient, in a year or so of babying your pan, you'll end up with a surface that seems more durable and smoother than I've obtained through other methods.
All of that said, be careful just to use a small amount of shortening/oil each time and don't use high heat or you'll encounter the problems mentioned in other answers.