Nexus client is awesome and easy to use. I definitely recommend starting out with it. It has all the basics you need for the start, much more easier to get used to a game when you can see chat window, inventory, main screen, what's in your room, and much more from one screen and you don't even have to do anything to see those. They're there automagickally.
I prefer Mudlet myself, but I've been using Nexus as well. Nexus using doesn't require coding experience which is a huge plus.
Fast summoners should be able to deal some kind of damage, pressure mana and deal afflictions all at the same time also. But I find diabolists better doing that. Fast summoners tend to be a bit less tanky than diabolists, but that's only my experience.
Edit. Fool tarot deals mana leech and can be infused with some noctu spells. And there you can also use unleashes when they're available.