How to open illusory walls with messages in front of it

There isn't a shortcut of any kind, unfortunately. Sorry. Confirmed in the Collector's Edition game guide.

As for the Chariot, it's really not that difficult of a fight relatively speaking. If you want some tips, see below.

As soon as the fight starts, begin heading to the left. There are skeletons that will harass you, but don't worry about killing them. They will be resurrected by one of two necromancers. Basically, just push around the area as much as you can, taking time to duck into the small alcoves when you see the chariot coming. The chariot will either kill or knock down any skeletons that happen to be harassing you. Keep sprinting toward the first necromancer and kill it. Then clean up all the skeletons around you. Next sprint toward the second necromancer and and kill it, then clean up the skeletons. Once the two necros and all the skeletons are dead, you should see a switch across from you. Flip the switch and the fight will transition into a much more traditional style boss fight. Good luck and remember that horses don't like it when you stand right behind them.

A big help is getting the ring of Binding: http://darksouls2.wikidot.com/ring-of-binding. This cuts down the effect of being hallowed, and dying multiple times.

I personally find the game slightly easier than Dark Souls, because of a lot better placed bonfires and the possibility to skip / bypass certain bosses. At least until your better geared.