Not all perks in a tree is worthy of investment. For example, with a little bit of time and looking up an ingredients table online, you can mimic the benefits of the three experimenter perks under alchemy.
My rule of thumb for all the characters I've made so far is not to aim for the end goal of 80 perks, but try to 'complete' the build at around 50 perks, and then use the other 30 for padding for interesting looking perks and skills.
Here is how I break it down, using my sneaky archer assassin as an example:
- 1 primary tree for combat: I decided to go with archery here to make my bows deadly, picking up every perk except Hunter's Discipline, Steady Hand and Ranger - 12 perks
- 1 secondary tree for combat (don't need to max this one out): I went with one handed, but is only going to get the 5 + damage perks as its mostly to boost my backstabbing damage with my dagger. - 5 perks
- 1 defensive tree (light, heavy, or alteration): I went with light armor, but only for the + armor rating and 10% dodge perks - 8 perks
- 2-3 utility (none crafting trees):
- Sneak - 4 perks to get to the 15x dagger backstab
- Illusion - 4 perks to get to quiet casting, 3 to get to expert illusion for invisibility
- Pick pocket - 4 perks total to get to extra pockets and poisoner
- 2-3 crafting trees
- Alchemy - 7 perks for alchemist, physicist, and benefactor to allow me to make max effectiveness potions (but not poisons)
- Enchanting - 8 perks to max out effects and to get to extra effects
- Smithing - 2 perks just for arcane blacksmith. I plan to wear only leather armor and use steel daggers (mehrune's razor, which I plan to use is a steel dagger).
Total perks: 54
I will have maximum crafting effectiveness via alchemy + enchanting feedback loop, which allows me to craft a set of leather armor with maximum armor rating and a steel dagger that can easily 1 shot anything in a sneak attack. Also, the nightingale bow (which I plan to use) does not require the ebony smithing perk, which is a nice bonus.
If you want to use a different bow, spend 3-4 more perks into smithing, but you'll be done by level 60 rather than level 80, which is much easier to do.
Afterwards, the filler perks will go towards thing such as magika regeneration (restoration tree), spell resistance (alteration), etc.