This is a very difficult topic and there are plenty of thoughts and blog posts available online. The need for a lawyer probably depends on whether you intend to raise capital or just see it as a short term project? For bringing in new founders you should look at some sort of vesting agreement to vest founders over time.

For general equity-split, the calculator below is thought provoking: http://foundrs.com/

However generally with two founders a 50-50 split is best as both of you need to be 100% committed for it to work out.