How is support calculated when parents share physical and legal custody and parenting time equally?

You have a couple of different questions-- so I'm going to take them in order to make sure that everything is covered.  Indiana does have child support guidelines that are based on income.  However, judges are free to deviate from those guidelines if they can articulate a good reason for doing so.  If both parents are literally providing care and support of the children "fifty-fifty", then yes, the court can take that into consideration to reduce or eliminate a child support obligation.  There is not a formula for what the support will be when the court deviates from the standard guidelines.  Instead, the appellate courts will look and see if what the judge did was in "just".  If a reduction or elimination of child support can be justified by identifiable factors, then there won't be problems with an appeal.

As far as the amount, if your income has changed, you can file a motion with the court to modify your support order.  Here is a link to the site by the courts in Indiana that will provide you a calculator and some guidelines as to the imposition of child support: http://www.in.gov/judiciary/2625.htm .  Complete loss of employment is going to be a basis of reducing the child support obligation--even if the judge won't eliminate it.

Finally, you raise a sub-concern about your attorney.  The link I gave you has some very good resources for people who want to represent themselves.  It does help, however, to have a family law attorney help you.  If this attorney didn't work for you, go shopping.  There are plenty of good attorneys that are willing to work hard to uphold your rights.