Taken from the OpenStreetMap License Page
You are free to copy, distribute, transmit and adapt our maps and data, as long as you credit OpenStreetMap and its contributors. If you alter or build upon our maps or data, you may distribute the result only under the same licence.
If you are using OpenStreetMap map images, we request that your credit reads at least “© OpenStreetMap contributors, CC BY-SA”. If you are using map data only, we request “Map data © OpenStreetMap contributors, CC BY-SA”.
Where possible, OpenStreetMap should be hyperlinked to http://www.openstreetmap.org/ and CC BY-SA to http://creativecommons.org/licenses/by-sa/2.0/. If you are using a medium where links are not possible (e.g. a printed work), we suggest you direct your readers to www.openstreetmap.org (perhaps by expanding ‘OpenStreetMap’ to this full address) and to www.creativecommons.org.
So I think the answers are, Yes you can use your data alongside OpenStreetMap, as long as you don't infer that your data is endorsed by OpenStreetMap. As long as OpenStreetMap are clearly acknowledged whenever there is an output. To be safe I would probably include it everywhere you can, it won't hurt, and anything that increases the profile of OpenStreetMap can only be a good thing.
More legal stuff can be found on the Creative Commons License Page
EDIT: In response to comment: From the OSM Wiki Legal FAQ
Can I charge for distributing OSM data or data derived from OSM data?
Yes. You can charge any amount of money you want for any service or
data you provide. However, since the data (or service) that is derived
from OSM data must be licensed as above, other people may then
redistribute this without payment.
What I take from that is that any OSM or OSM Derived data you plan to sell could then be redistrbuted by the buyer under the same license. However any data that is yours or under a different license is not subject to this restriction.