1. First you will have to tender technical resignation so as to get the past service benefits. In this regard, you are entitled to get the service in District Court as pensionable one alongwith the service you are joining through WBPSC. EL at credit will be carried forward to your new service. If your basic pay in District Court is more than the initial basic pay at entry level of your new service, then you would get pay protection. All these are guided by rules.
2. No seniority would be counted.
3. In the new department you will have to go through probation again. The duration of probation will be mentioned in your appointment letter.