Firstly, I'd like to say hi to everyone, as this is my first post. I've seen a second hand FU 1000 for sale but have also seen a 10 inch sony field monitor for sale. Both are around about the same price. Which one would help me more. Or which one should I purchase first. Thanks.

That will depend on how you shoot. If you need high moblilty, the FU 1000 is probably better for you. If always shooting from a tripod at a reasonably fixed location the Sony may be better.

Does the Sony need AC power?

The sony comes with a battery facility, but they are not included in the price. I thought it may be easier to use a small monitor, as most of my shots will be pre-planned. And I was thinking that the monitor would give me a better idea about how my lighting was working out. However the view finder would be great for mobility.

I've read a few posts on the FU 1000 and it sounds a bit tempremental on an XL1. Burn outs etc. But it does look awesome.