1) Your choice is all a matter of tastes and how you want to play.
Racast might be one of the strongest class that exists and a great team asset, high hp, high atp, decent ata and TRAPS (which are OP in ultimate).
The lack of buffs might be an issue on a few end game arenas in solo play, but you have workarounds ( zallure/demon's guns, a mag that provides Shifta /deband on bosses, PB Create unit).
Resta is not really an issue because you can generally carry enough mates for a run.
Ramarl has low atp and hp but her buff/debuff abilities make her a great character for solo play, confy everywhere.
She can also be a good Force replacement in a team and she has high enough ata to be potent with specials like Hell, arrest or demon.
Ramar is very strong too, he has extremely high ata and good atp: He is both easy in solo or team play.
His only weak point might be at low ultimate levels (80>120) when solo, he clearly lacks hp and gets knock down easily by strong mobs.(ramarl's jellen negates that issue partially)
Though he compensates with his high abilty to incapacitate his enemies with specials such as arrest, spirit, hell etc.
My advice: if you are new to ranger, go for Racast or Ramarl.
They are both easy to play everywhere and don't require high end stuff or skills.
2) It depends what you want to hunt: Purplenum, Yellowboze, Whitill, Greenill or Viridia might be good ideas.