It depends on the type of law practiced. For corporate or tort, it would be better to be with a big firm but it is also more pressure. For family it would be better to be alone or with another lawyer.
For criminal law, it can be either or. But if business really takes off, you could be stuck turning clients away or referring them. Most lawyers give referrals to their friends anyhow but you might get a reputation for turning away clients and then your own business falls off. That is why it might be best to have one other with you. You can also split the overhead.
I doubt a lawyer would take a percentage of profit deal.
Many would offer 1hour free consultation.
I suggest you find someone who is established and works locally. In the early stages you may have to visit them many times. It is easier to visit someone locally, then visit some guy who is miles away, has loads of clients and charges big bucks.
Have any school / college friends become lawyers?