Ash - Offensive stealth, Shorter invis but can kill everything, bit of a selfish frame as not much team comp usage, moderately squishy Loki - General stealth, longest invis and can disarm enemies, good for endgame comps, squishy Ivara - AMAZING amount of utlity, Invis gives increased headshot multiplier but you walk slower. Good for solo or coordinated teamcomps, squishy

Best bows ingame at this point are the Rakta Cernos and the Dread. The Rakta you can get from the Red Veil Syndicate after you rank them up to the highest rank (also you have to be mastery rank 12). The Dread blueprint drops off the Stalker, a boss type character who will randomly attack you after you receive a death mark from killing bosses. Rakta - faster draw time, less crit, has syndicate elemental damage and effect - Overall extremely good Dread - OMG CRIT - needs crit build but extremely powerful. Slower draw time

Best secondary for stealth gameplay would be a toss up between the Hikou Prime, Despair and Spira. Hikou Prime you need to farm the void for parts and craft it. The Despair blueprint drops off the Stalker and the Spira you can buy the blueprint in the market for credits.

Hikou Prime - Shuriken, very fast throw speed, low damage, good with concealed explosives mod. Despair - Overall good all rounder. Nothing special other than high damage. Spira - slow throw rate - high crit chance so low DPS overall. Good single target damage.

Daggers have a covert lethality mod that adds 100 extra damage for all stealth finishers. Dark Dagger is probably the best considering it also has a Syndicate mod called Gleaming Blight (also from Red Veil) that adds more damage in general. You can also check out the Redeemer, a hybrid shotgun gunblade that in most cases is kinda bad, but when stealthed actually becomes an extremely powerful gun type weapon.

Shade is good, The kubrow breed Huras is basically the same thing. Both are good (note, sentinels can die easily.)

Yes, play with all sorts of weapons to find what you like. The more weapons and warframes and things you max out, the more mastery you get and the more your rank goes up. The Venka (claws) are a rather mediocre weapon, not really endgame material. But they are fun and the stances for them are quite nice.

Hope this helps.