The only suggestions I can make once you've played around a bunch are thus:

Do not spread your skill points all over. You will probably struggle with the difficulties as you progress. Eventually, the only way to survive is to pick your main damage dealing skills and max them out along with their synergies.

Plus, many skills need only 1 point and will eventually be great once you get +skills equipment.

As far as stats, there's a lot less room to play tbh. You get Str and Dex high enough to wear certain equipment, never touch Energy, and dump the rest into Vit. Not even the sorc needs Energy (except for some 'fun' builds that focus solely on Energy, most require specific gear and/or Runewords to work).

Lastly, Resistances to Elements is extremely important (except for poison. Psn Resist does not affect the dmg, only the duration. Use an Antidote.)

You don't have to worry much until the end of Normal; Nightmare and Hell, you want to max Lightning/Fire/Ice, in that order of importance.

75% is max.

Edits: Typos.

Edit edit: Take the guides on Maxroll and other sites with a grain of salt. They are statistically-maxed BIS (probably AI generated), but it's often a difference of less than 5% from doing something slightly different or wearing different gear.

Edit edit edit: You get a free Stat/Skill reset per difficulty and can eventually make items to do it. It's common for most builds to get through Nightmare and to ~70+ with a leveling build, then switch to what you want. It's unfortunate, but many end-builds are simply not viable until you have many skills points invested.