Advice on mod direction

[IceMountain]

Ok, here's the background:

My ex and I live about 4 hours apart in different states.  We have a 7 year old son and are both remarried.  We were in the process of modifying our original decree, but there have been several changes that are affecting where we go next.

1.  I fired my lawyer 2 weeks ago.  He was completely incompetent and did not follow through on filing motions, etc.  I have requested my complete file from him, but only received info I sent him and copies of 2 motions that were filed with the court.  He did not include any notes, correspondence, other motions, etc.  So I am sending him another letter to request that info.  

I now need to retain a new lawyer, but have to save the retainer fee before I can do so.  Is there a specific time frame I need to follow in retaining new counsel in Iowa?

2.  I have changed careers.  After 2 years of being in and out of unemployment I have completed an educational course and obtained secure employment.  The only downfall to that is I will now be away from home for about 1 1/2 weeks at a time, which definitely affects my visitation with my son.  And, yes, I did consider that before choosing my new career... but I need stable income in order to support my son and my current family... it's a double-edged sword, but I will only need to travel extensively for the 1st year of my employment and then I will be able to be home more.

So, now, I don't know where to go next with the modification.  Do I continue with it now?  

3.  The reason for the mod is that the original was done when my son was an infant and me and my ex lived within 1/2 hour of each other.   Since the original decree my ex and I have both moved, in opposite directions of each other.  The travel distance has changed things, especially with pick-up and drop-off and holidays.

4.  To be fair, my ex and I do seem to work things out ok.... but usually only as long as it benefits her.   Things have been ok for the past 6 months since I retained a lawyer.  But, now that I fired Mr. Incompetent, she has already started playing games with traveling, etc.

5.  My last question is this.... I currently have my son EOW.  If I am not available on the weekend, can my wife (my son's step-mom) exercise the visitation?  Or can my ex deny that?  I plan to offer some of the weekends to my parents, but I don't think that will be a problem with my ex because she gets along well with them.

Sorry for the long post.  I just really need some direction and advice as to how to proceed.

Thank You,
Ice Mountain