1) Send only those documents that are mentioned in checklist
2) No need to send job experience letters or financial statements. If they require they will ask for it later. Their website clearly says to send ONLY documents that are listed in checklist
3) There is WEB FORM to communicate with them, however, they won't answer if information is already provided in their website
4) It is better to maintain the employment so that IRCC Case Officer does not find any thing different from SINP file. In addition, if there's any change in your employment status, you need to notify the same to SINP office as the Nomination Approval letter says "You must contact the SINP to inform our office of any changes to marital or family status, change in address and change in employment prior to receiving permanent resident status."
Hope this helps.