Day 1: When did you start trading? How did you end up getting into it?
Depends. Trading what? In June 2007 I joined GameFAQs for the first time solely because of the Diamond and Pearl Trading Boards. Sure, I was "trading" at that time, but definitely not heavily trading. I had about a dozen events and probably less than a dozen shinies on my Diamond cart before I lost it in November 2008. May 2009 was my first real exposure to the trading scene because I started heavily event trading. I traded 30 of my Distant Land Pokemon for 30 random GBA events such as 10JAHRE. I ended up getting picked up by Pokemon Secure to get my event legit checked, and that was the start of me collecting legit events.
Day 2: Most recent Pokémon you traded? What did you get in exchange?
Today, I traded a proofed CHT PC Tohoku Victini for a proofed SPA Lillie Vulpix. Before that, I traded 10 proofed gen 7 events for CHT/JP PC Tohoku Victini and FRA/KOR Lillie Vulpix.
Day 3: What's your favourite Pokémon? Have you ever traded for it?
*looks at sig*
Lugia, of course! Uh... Of course I've traded for it? I have every Lugia event, I have multiple Shiny Lugia's, I have a few proofed event Lugia's, but my trading philosophy isn't determined by what my favorite Pokemon is. If you want to even complete your Pokedex, of course you'd have to trade for it.
Day 4: What is your favourite Shiny Pokémon that you own and did you have to trade for it?
My favorite? Hmm... I think the one closest to my heart would be the Shiny Thundurus that was RNG'd and personally given to me by Flan. Shiny Thundurus was by far the hardest shiny legendary to find legit. I've went through around 8 hacked Shiny Thundurus before Flan got their own and gave it to me.
I'd say my most valuable shiny is my personally obtained Shiny Manaphy. In March, I found a Manaphy egg in my Platinum game from 2010, and at that time I only had one legit Shiny Manaphy that was personally given to me by Kaphotics himself, he RNG'd it and gave it to me. I RNG'd my own Shiny Manaphy by trading it to my SoulSilver cart (because the only way to legitimately get a Shiny Manaphy is to trade the egg to another game and let them hatch it, you can't hatch it on the game you obtained the egg in).