I just recently completed the Hoenn Pokedex. The good 140 hours on my Emerald file are the result of filling out this Pokedex. At first I wasn't going to do it because I thought you needed to get all 202 Pokemon... including those last two, which are unavailable except for in those events... but once I found out you only needed the first 200, I actually decided to go for it.
I had to get Pokemon traded from my friend's Sapphire game, my sister's Leaf Green game, and a Ruby game I rented. After I got all the basic Pokemon needed for the Pokedex, I had to put up with several dozen painful hours of beating the Elite Four, so that I could evolve these basic Pokemon (they were holding Exp. Shares). The only good news is that a few of my good Pokemon gained several levels through this repeated Elite Four battling. My Lapras, which was at level 51 when I traded it over from a rented Fire Red game, is now at Level 92. It reached this level almost completely on shared experience.
Feebas was a huge pain to catch. I had to start at the top of Route 119 and fish 4 times on each tile. Fortunately, I ran into a Feebas-yielding tile after less than an hour. But... that was on the third or fourth Feebas hunt. On the previous Feebas hunts, I had been searching for several hours with no result. When I hit that Feebas-yielding tile, I just kept catching Feebas until I got one with a Beauty-increasing nature.
Another big pain was Latios. I always choose Latias in Emerald... which was a mistake as far as completing the Hoenn Pokedex was concerned. Latios was pretty much the reason I rented that Ruby game. I got some other Ruby-exclusive Pokemon out of the deal, though... Zangoose, for example.
The rest of the legendaries were no problem. I actually had two Master Balls to use. I had previously rented a Fire Red game, and had gotten the Master Ball... but hadn't used it. When I had to return the game, I made this random Pokemon hold the Master Ball, and traded it over to my sister's Leaf Green game. The Master Ball-holding Pokemon eventually made it over to my Emerald game. I used the two Master Balls on Groudon and Rayquaza... but I had to catch Kyogre with an Ultra Ball.
The only other Pokemon that was a headache to obtain (besides those Pokemon that evolved at painfully high levels) was Crobat. I caught the Golbat at level 33, and it didn't evolve until level 58! ._.
The very last Pokemon that I added to the Pokedex was Metagross.
I picked Cyndaquil of course (I love fire Pokemon)... I'm currently raising it by fighting Pokemon in the grass and caves. It's boring, but at this point in the game, all the trainers I can fight have Pokemon that are way out of the level range. Right now it's at Level 26.