Now, levelling up is much faster since monsters level up with you.

If you prepare yourself in the right way:
- Old Hellfire ring possibly with +damage bonus ( there is no level requirement to use it. Also the +dmg modifier does significant damage upgrade for a low level character, which helps quite alot)
- Ruby for helm and low level socketed weapon (even a low level yellow weapon with native socket and damage rerolled with a level 70 roll by the mystic)
- other low level rare items with level 70 rolls
- you want reduced level affix so you can equip a stronger item much sooner. This helps you through most of the leveling process significantly

I think you can start the game at torment 6 then scale down the difficulty when monsters become too slow to kill (or hit too hard)

That way you will probably reach level 60 (don't know about level 70) before act IV
lv 1-5 = have a friend bring you to act 2 to collect the books from the inn, and at kassim's outpost. This will level you up to 5.

Next step is probably to just quest until your lv 25.

At 25, you can ask your friend to power level you at cota, and everytime you reach the level to unlock the next difficulty, have your friend help you kill the bosses to move up acts.