I'm only on a 5 year plan because Mazz, Matt, DaveW and a few others told me I was. Twice.
1) Do you compose for listings?
Yes. If nothing else, it hones my ability to focus on specifics. That in itself is worth the price of Taxi admission.
2) Do you resubmit your stuff to mulitple listings?
Yep. I have 2 main groups of music: specific writings for exclusive targets, and writings for calls etc that will remain non-exclusive (unless money talks, of course...). Oh and, gratuitous self-absorbed music for my own personal head space - I don't write enough of this in my opinion (but probably share far too much of it!).
3) Do you submit outside of taxi to libraries?
Yes, but very selectively. I've had a couple of experiences that were not too far from the negative side of the dial, so I pay attention and never let a file out of my hand unless I've had a convo/thread with the target. I used to spam my tracks, but frankly... it's too much work, they probably didn't get listened to, they didn't get placed, and to be honest, I doubt they were that good anyhooz. I'm waay more selective now. (And hopefully producing betta music.)
4) How do you manage the cost side of things? Do you tend to do all playing/ singing yourself?
I do everything, including midi drumkit, and vocals often, and bring in people when I need to. I have no problem paying a session player, and don't pay much attention to ROI for a given track. If it comes out cool and I dig it but it's absolutely not something that will get placed, I'm okay with it - for me it's about the music, in whatever shape that shows up as. (The caveat is if I am 'focused' - see above.)
5) Do you focus more on instrumentals?
Yes, mostly instrumentals, but I love to sing. And while I'm not great, I have fun and smile quite a lot. Mostly people don't leave when I do, so I feel that's a pretty significant bonus.
6) Do you maintain websites etc outside of Taxi?
I do, but frankly I could care less. I don't really maintain anything because it will always need maintaining then: websites = time. I don't have a FB user account (though I have a band account), and my online experience is most often either work-oriented or music focused. I do have RN, SC, and probably some other stuff I've forgotten (back when I was spamming, see above). (SC is good for pitching sometimes, depending upon targets.) This forum, while different than FB I admit, has a much higher level of value to me than tweaking out my web pages, or 'liking' this/that/the other... (near-rant over).
Besides, it's not about how far the bus is going, it's more about just getting on the bus, IMO.
Hope this all helps.