April 11, 2015 9:35 PM EDT
I guess maybe I do this backwards. I really don't pick a level. I decide what skills I want, about how far I figure they will get leveled and then figure out how many perk points I have to work with (using the attached chart and some guess-work). I figure that speech and lockpick will always get leveled, but count those together as one skill, unless one of them is going to be significant to the build. I generally find that I use between 4 and 6 skills which puts me in the mid 30's to mid 40's for most builds.
That said, if I can't find a use for all of my perks, I have no problem stopping early. I have one build that is only a level 18 build, even though I could eventually max out two skills (and thus have 24 perk points).
I have never messed with making skills legendary, because I find some of the fun to be figuring out how to make the build viable if the perks I want outnumber the perk points that would be available.