With the class system and it's 7 main skills a thing of the past, and perks the thing of the future, i was wondering how many skills it would be advantageous to invest in for a given character. You only have so many perks, so you obviously don't want too many skills, but you also need diversity; you can't just pick one or two.

For example, if i wanted to make a thief/assassin, then the first thing i would obviously need to invest in is sneak. I'll need one-handed for dagger stealth kills, and archery for when it's impossible to get so close. For those occasions in which i'm caught or (rarely) my stealth kills are not enough, i'll need light armor to protect myself in combat. With light armor comes smithing, if i want very good armor. For the thief side, pickpocket and lockpicking would be good to invest into as well.

So in all, thats sneak, one-handed, archery, light armor, smithing, pickpocket, and lockpicking. Coincidentally 7 skills. Is this too many skills to invest my perks in? Not enough? I realize you can pick and choose how many perks you put into what trees, but i'm just looking for an estimate on an ideal number of skills. It's kind of confusing for me to prioritize what skills to pick, and if i should pick them at all.

My lvl 55 sneaky character have perks in six trees - http://skyrimcalculator.com/#22011. Many of the trees are rather worthless (speech, lockpicking, pickpocket), or some induvidual perks gives too little bang for the buck (Stealth beyond the first, for one).

I think the obvious answer is you don't need to max out all the skill trees for a given tree if you don't need the skills. I was working on the lock-picking tree and I got the perks up to "find 50% more gold" and "50% improved chance of finding rare loot" and then stopped. At that point the perks for "easier expert/master locks", "lockpicks never break" and "lockpicks start near the sweet spot" were all kind of pointless because I had gotten so good at the mini-game that I rarely break more than 5 picks on expert or master locks and I always have well over 100 lockpicks.

you have 80 skill points to use till you hit the level cap, so its no problem, my main character is lvl 49 and i have all i need in block, one handed, destruction, heavy armor, enchanting, smithing and now im starting to play with 2 handed weapons xD and also there are many perks from the skills that you decide to use that wont suit you, or will be just useless for you playstyle. with 4 main skills you will be all set by lvl 32-25 maybe and with 5 by lvl 41-42 atleast from my experience xD

You only have 80, I assume you mean perks, if you max all attributes to 100 though, so I wouldn't rely on that number to determine how to plan out your character unless you plan on maxing out everything.