Is it good for a newbie to start with Sylvan Deck ?
Sylvan is quite difficult to combo for newbie but if you can handle it then buy it. 4 first pack in this game is still good. The other are Valkyrie's rage, Crimson Kingdom, Generation Next and Servant of Kings. They're versatile either for farming or compete in PvP
i'd suggest going with aliens for now they are one of the stronger decks and are easy to get you just need to buy abyss encounters pack and all the important cards are either normal or rare
I expect it to be nerfed but if you want a currently strong easy KoG viable deck you could go for it.
I personally would invest in something else that is probably more longterm.