Hi Terri
Point 1: Family history is a hobby - you do it for your own pleasure - so research whoever you want. Much more important than *who* you research is *how* you research. Make sure that every fact in your tree is backed up with original documentation and that you cite your sources properly. Never copy something from someone else's online tree. If you find someone else is researching the same family, make contact with them and offer to collaborate.
Point 2: The best way to deal with a brick wall is to go round it, not bang your head against it. Researching the wider family can often provide invaluable corroborative evidence.
Hope this helps
Caroline