How add dynamic approvers who are not part of default workflow Adhoc approvers

hi

i am new to workflow.

my requerement is

1.To add dynamic approvers who are not part of default workflow approval chain but selected at run time by Approvers?

                                Any user can add adhoc approvers at runtime and sent work item to them.

2.How to send Alert notification like  workitem is 2 days old .and next 5 days old and 7 days old.

Please tell me how to acheive this. ASAP.