[*] He's super good into most melee match-ups except for the obvious fiora, Jax, etc. but is a pretty good pick imo
[*] He is just super vulnerable early if you misplay alot
[*] His sustain in lane is ok, with doran's blade and mega hp regen you should be fine, just manage it the best you can.
[*] He's quite a different champion to play. doesn't really dominate lane unless you get to harass and farm as you please.
[*] In mega, if you don't go in and do your job of cc'ing the most you can, and misplay, it will go in the enemy's favor real soon.

[*] Look for multi champ ults, bait them into choke points or walls, it should be easy to get in with e to transorm into mega for those multi champ ults, and flash if needed.
[*] If you miss ult, try and at least get a mega w onto a squishy or someone you don't want in the fight asap.
[*] Poke as much as possible with your q and get as many mini w procs you can.
[*] Slowing them with your q in mini is so important when trying to get the ace, or escaping. Although sometimes turning around to q isn't the best idea, it may be better to just keep running away.

Some people will max their w first, using it's passive alot. But I'm sure the q max is better because of the raw damage and the slow helps to get the w passive procs anyways. Maxing e second is also better imo, instead of maxing w second. Again, aa'ing faster because of the attack speed boost is much better than the hp% you get, it's not that huge to try and go for it. As for ults, whenever you get the chance to is the obvious choice to put a point in the skill slot.

I used to rush boots in s5 for some reason I just thought it was good, I saw it in the LCS with some Hecarims and I would rush them with Homegaurds too. Then I would rush Black Cleaver. However, this season, or pre-season, rushing Black Cleaver is key. Against Vladimir, Akali, or maybe even Rumble if somehow you have a tough time in lane, getting a Spectre's Cowl is not so bad and probably the best choice instead of Phage. After getting that you can definitely rush Black Cleaver. Maybe get Mercs too if you can spare the gold. The same goes for AD oppenents like Darius, Trundle, or Fiora. Getting a Chain Vest and then Phage is perfectly fine, even if you're backing after killing them. The more you have in terms of survivability is key vs these opponents. One last thing, getting two Doran's Blades before any component to an item is fine too, just make sure you are confident in what you will be doing and how you'll be doing it, in lane.