Well, IMO that bow as it is now is not very good. The longbow fires too slowly to make good use of Vampirism. Get an elemental, sundering, or poisoner's string for that bow and it would make a good pulling bow. I can't really tell you what makes a good Ranger secondary, as I have a 20 R/W but I only use Ranger attributes and skills.
Yeah, the ranger does pretty good alone. If I was to pick a secondary profession, I would consider the monk for the earlier reasons. I would also consider the Necro as well, since you could be draining life with your Life siphon to keep your health up, while draining theirs, and shooting them as well. Not to mention, your pet, plus a few undead help the odds in a fight.