I have never used anything but hop pellets. I wish I had an option, but my LHBS doesn't carry many varieties of whole hops. I always compensate for the wort I know I will lose. Its probably about 2-3 liters for me every time.
I try and get 6 gallons (~23 litres) in the primary so I can get 20 solid bottles. It's often hard, and there was a whole lot more gunk that was transferred into the fermenter just because of the hop mass. With whole hops you can just stick a sanitized strainer at the liquid level in your kettle and none of it transfers. I guess it'll settle out in the primary and hopefully won't make it through the secondary into the bottle.
I've been too lazy with my hydrometer... and just because it reads zero at zero doesn't mean it's right, either. True test would be to do two known solutions like a 1.000 and a 1.090 or something like that.
If I were to upgrade my gear, I'd get a big pot and a burner. You'll get better utilization out of your hops since you won't have to dilute the wort coming out of the primary.
In place of a chiller, you can just be a little short on your liquid level and add a block of ice. Seriously, it works wonderfully in a pinch.