Hi Jaydeep, Welcome to TAI
I just came back from Mumbai yesterday and I took the same route. Trust you will not find any better road anywhere.NH4 till Satara is well maintained, but after that there would be potholes and the road is not as smooth as the roads that you find in Karnataka. to answer your questions,
1. I tanked up in Bangalore and had to only fill up Petrol 10 kms before reaching Pune in a HP bunk. Not sure of other bunks which are safe to be filled,as I found this to be fine.
2.Deviations are there till Chitradurga, but not many, if I may say. There are proper road signs and the Deviation road also is pretty good.
3. Best thing is to leave early morning around 4 or 4 30 so that you can reach Pune by 5 30 6. You can have Lunch in Belgaum. Has a very clean and good restaurant adjoining the NH4 called as "Sankam". You can see the name of the restaurant from the Highway itself. So once you reach Belgaum, take the service road and you can have a good meal there. You will reach Belgaum by 1 30 ish. Be vary bout bullock carts and tractors coming on the wrong side, although they would have given the correct indicators, it takes atleast 3 to 4 seconds for us to realise that there is something coming on the wrong side.
Let me know if you would require any other assistance and I would be happy to help.