well, seems like u got ROW version. that means you can switch the voice from ENG to JPN and vice-versa bro.
but for this series, the ENG voice is not bad at all.

downloading forever with screamyx 2mbps...

extra 20GB for voice dub

No farming needed until Eden. As long you don't intentionally skip/sneak by any mobs along the way to Eden, go with the Ceith stone mission flow of number, your party members crystarium growth should be on par to any mob or boss you meet.

As [d]-ky said, no need to invest in non-innate role first. The growth value per CP invested not really worth it. The only non-innate role  I go for is the medic and nothing else to boost healing augmentation value of other main healers when I need speed healing in MED/MED/MED.

There's no fixed role for each party members. All their 3 natural roles are very useful when used at the right situation, timing and combination. Go wild and experiment them and see what combo suit your playstyle. Here's some of mine (just a tip of an iceberg, there's whole lot more combination I got):

Sazh/Hope/anyone
Sazh as commander is good against enemies that move around alot or have high evasion properties. Sazh/Hope opens up a combo for speed synergy build up when enemy is immune to alot of debuff. Don't autobuff when you're controlling one of Sazh/Hope, go manual control so both won't like cast haste on the same party member.
COM/RAV/RAV (Standard battle starter)
RAV/RAV/RAV (Speed stagger meter build up)
COM/MED/MED (Speed heal + holding stagger meter, works well with triple RAV)
SYN/SYN/SAB (When enemies are tough)

Fang/Vanille/anyone
COM/RAV/RAV (Standard)
SAB/SAB/RAV (For speed success debuff, 2 SAB have better success debuff rate than 1 SAB. Remember that role bonus affect other members too, not just self)
COM/MED/MED (Speed heal)
SEN/RAV/COM (To survive mass mob, if you still haven't got any 3 ATB nukes)
SEN/MED/COM

Light/Snow/Sazh
COM/RAV/RAV (Standard)
RAV/RAV/RAV (Speed stagger meter)
COM/COM/COM (If only one staggered enemy with at least 500% staggered status)
COM/SEN/RAV
MED/SEN/SYN
MED/COM/RAV

Battle tips:
- When enemies are tough, don't hesitate to start off with SYN+SAB with no offense at the beginning. It pays to be prep up for the kill. Debuffed enemies contributes to the speed of RAV building up stagger meter, even more so when you hit them on their elemental weakness after imperil debuff.
- Abuse that launch effect skill whenever you can (either by COM or RAV). Launched enemies = semi-dazed enemies. They can do nothing to you (or themselves) in this situation. Launched enemies are helpful to stagger meter build up too.
- When dealing against a single enemy, prioritize SAB over SYN. It's quicker to debuff 1 enemy than buff 3 allies. (Only applicable if enemy is not immune to debuff and you can survive their nukes if any.)
- Don't rely fully on "auto"-battle. Occasionally you'll need to go manual to control the battle. Recognize when to hit early/late, when to nuke, which enemy to aim (position awareness), which buff/debuff to prioritize. Control the battle well and you'll be awarded with 5-stars rating where auto-battle could not.

only got Steam achievements. It doesn't have same function as PS3 trophies.

still there, can unlock same way as you did in PS3. just the achievements doesn't weigh as much as trophies IMO.