The later developed programs like LimeWire, Phex, GTK-Gnutella tend to use less over-head when running as ultrapeer. I think this is because they compress the messages sent to and from other clients that can also receive and send compressed messages, thus less bandwidth used. There's probably other reasons also.
I think the standard ultrapeer bandwidth is between 5 to 10 KB/s for the above mentioned programs, perhaps a fraction more.

Depends upon your overall bandwidth abilities I guess. I only have modest upload capacities since most standard ADSL2 upload abilities in my country are not especially high. Yet I choose to run as ultrapeer quite often. Some years ago I deliberately did not run as ultrapeer due to similar bandwidth concerns as you. I was only on ADSL1.

In the past, some people might have advised one or the other depending upon which way you wished to help the network the most (unless you had a very good upload ability.) But these days I think it is more dependent on your client and your bandwidth abilities and how popular your files usually are.

My personal advice would be not to worry too much about it. If you have 50 KB/s or higher upload capability, I think you can safely be a large'ish sharer and an ultrapeer.

Off-topic: If you wanted to attract attention to any particular shares. There's a few ways to do it. One is via file description (if it is not an audio file.) Another is to do searches of the same topic of your shares. This brings you in contact with those also seeking such similar file topics. A tip I picked up from experience.