Hello Mr Empika Sir,
Since you're new to Unity, and you're a coder, I'd recommend doing it without PlayMaker to start with. You can easily refactor later.
Since I've started using PM, I've found that while it's possible to do pretty much everything with it, it's real power lies in using it in the right places.. which is kinda hard to define. A mix of US/C#, multiple FSMs, and custom PM actions seems to be the way to go.
If you're making a turn based battle system, you'll probably find that PM is great for handing all the game states, and also all the character states, using multiple FSMs.
The UI *might* be better scripted from scratch though. Particularly as the built in GUI in Unity leaves a lot to be desired.
Re: the GUI, use NGUI for now. There's a free version on their site, which might be useful.