First degree arson is a first degree felony, 30 year maxium. However, with that criminal history, I'd be willing to guess that he can be habitualized, which would increase the maximum to LIFE. The criminal mischief over $1000 is a 3rd degree felony, 5 year max.
The answer to this question depends largely upon the defendants total points on the criminal punishment code score sheet. The first degree arson holds a maximum penalty of 30 years in prison. The minimum sentence he is facing depends again upon the score sheet. From what was stated in the question, the prior record of this particular defendant would appear to result in a relatively high number of points if the prior crimes are still scoreable. There also appears to be an issue of who actually set the fire that resulted in the charges. As this defendant does not appear to be the one who set the fire he apparently is being charges as a principal to the offense. Please consult an criminal defense attorney immediately as these charges are quite serious and will more than likely result in a prison sentence.