How much of maximum total current ( from all I/O pins including 5v pin) can be drawn from the arduino so it doesn't fry?
The data sheet says the limit of the power pins is 200mA, so with an individual pin not being driven harder than 40mA you can work out the distribution of current. There are also a number of other restrictions, see section 28 of the data sheet for exact numbers.
according to Ohm's law input resistance of arduino is greater than 10 Ohm. Right?
Well it is a sort of meaningless calculation. You don't talk about the input resistance of arduino, because a resistance is fixed. The current an arduino takes depends on what it is doing, how fast it is going and what loads it is driving. It changes all the time so reducing it to a resistance is of no help to anyone.
If you use a 7V supply (2V drop) you can draw 1A.
See this for how to work it out:-http://www.thebox.myzen.co.uk/Tutorial/Power.htmlhttp://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html