Firstly the long distance adjustment and the overall financial condition adjustment are discretionary with the court.  The Judge will need to approve the amount, but you are correct that if you'd like to formally request that credit, this is the box you want to put it in.  From the sounds of it, the distance adjustment would be applicable to your case.  The overall financial condition adjustment is more for considerations that fall outside of any other section of the guidelines.  One such condition might be that you require therapy or special education to cope with your learning disability which absorbs a lot of your income.  In such a case, the Judge could allow your requested adjustment (or make changes to it).

To calculate the amount, you would itemize all the costs to exercise parenting time (such as airfare costs and lodging).  Then multiply that by how many times you'd be traveling to see the kids over the course of a year and divide by 12 to arrive at the monthly amount.

It is possible the Judge could reject your proposal if you voluntarily moved to TX and there was no agreement to this move.  However, if the move was for work or to have family support, or possibly the move was already in the plan before the divorce, a Judge might allow it.  In my opinion there is no harm in requesting the adjustment.  The judge could allow it or not.  It's probably worth at least asking and making your case.