You may not need to flush or add a suction side filter, since you did change oil to ester. That is necessary only if the compressor blew. In that case the system has contamination all through it that will ruin the new compressor. Since you put in ester at the time of conversion, you may be "good to go". If you want to be safe, add the suction side filter. The flush is not very expensive and available from any a/c supply house. It is basically alcohol with some additives, it smells like orange. You will need a way to spray this through the lines. Since you would have the lines and everything apart, it would be a good time to use green o-rings since you should replace them anyway. The green ones are supposed to seal better with r134.
You should be able to find out where to get a suction side filter and any other auto a/c advice at www.aircondition.com.
Have a great day,