Current NAV -You cannot get the current NAV as the NAV's are declared at 8:00pm. Secondly, to invest and get today's NAV, your application should be logged in to the AMC's system by 3:00pm, else you will get the next day's NAV which will be declared at 8:00pm the next day.
Cancelation of SIP - Yes, you can cancel your SIP anytime you want. I am not clear about ICICIDIRECT, I mean how I is done there but if you had applied for SIP offline, then you have to intimate your bank to stop the ECS/PDC's and a letter should be given to the AMC for stopping the SIP. Please note, that the intimation to bank and the AMC should be done prior to 21 bank working days. Another thing is, if you stop the SIP before six months, there will be a deduction from the AMC's side along with STT. The deduction rate varies from AMC to AMC.
Flexibility in SIP -
As you mentioned about the flexibiltiy in SIP should be there, in Reliance Funds SIP you have three choices:
Rs. 500 for 12 months
Rs. 1000 for 6 months
Rs. 1500 per quarter
You can chose any of the option for the SIP. These are the minimum amounts for the minimum period required.