I can help with a couple of these.
Originally Posted by visus
I have to change flights at NEWARK LIBERTY airport for SFO. Now will my port of entry be newark or sfo? How to go about changing? Is it like just go for domestic change or what? Can anyone explain?
You go through immigration at Newark, show your passport and "enter the United States." Then you reclaim your checked baggage and take it through customs. After clearing customs you re-check your bag onward to SFO (there is a re-check desk right there, beyond the barrier) then proceed into the domestic terminal and locate the gate for your onward flight. Hopefully your schedule allows for at least three hours to accomplish this.
Originally Posted by visus
Also how many hours before, for each departure from india and departure from usa, should i arrive at the airport so i dont have to hassle?
At DEL I would say at least three hours. I haven't been since the terminal was improved but from what I hear things can still be chaotic. At SFO two hours before departure is fine.
Originally Posted by visus
I have exchanged currency, but they were only having 100$ bills. So can i know what's the best way to get change, that is in smaller denominations like 1$, 2$ etc. Can we change at airport with/without expenses or buy something and get the change?
You are not going to make any friends trying to buy a $1 candy bar with a $100 bill to get $99 in change. You only need to break one $100 bill while en route, for small expenses, cab, and tips; try the currency exchange booths (Travelex, etc.). When you get to your hotel the front desk can help you break the rest. $100 bills are not great everyday currency unless you re paying big restaurant tabs; the $20 bill is everyday currency. We don't have $2 bills.
Originally Posted by visus
Also I would get only 1:30 hrs in between my flight for SFO, will i be able to clear everything in that time or anything else that i need to know? ...if i miss the connecting flight, how to overcome that situation? Who will arrange my next flight?
1 hour 30 minutes is potentially not enough, especially if your incoming flight from DEL is late. United overseas flights are prone to delays and immigration / customs lines at EWR can be long. If you miss your scheduled EWR-SFO, United should rebook you onto the next available flight. EWR-SFO flights run frequently, every hour or two. If you emerge into the domestic terminal and you know you've missed your onward flight, go to a United service desk for a new boarding pass.
Originally Posted by visus
Also while exiting US, i have the reverse pattern from SFO-NEWARK-INDIA in that case what will be my exit point and where i have to submit the i-94 form, sfo or newark. And at sfo, do i need to go for domestic departure or international?
At SFO you must show your passport and I-94 at check-in but there is no formal exit-the-country barrier for departing international passengers such as you find at DEL. Domestic and international departures are commingled.