Are Bitcoin transactions traceable?

I have a question after a silly discussion.

We discussed for the best way for terrorists to get money. I have offered bitcoins. My question is: is it possible to trace who has cashed out bitcoins into money if you know the bitcoin wallet address.

I think it should be possible to trace, but how to trace such a thing?

NOTE: I’m just talking about cashing out bitcoin into money, not buying some cheap stuff.

bitcoin donations tax deductible?

I work as a volunteer for a tax exempt organization in the US. We are currently accepting donations in bitcoin but not issuing receipts for those donations. I would like to start issuing receipts. Is there any legal guidance available online about this? I haven’t been able to find anything.

Are Bitcoin transactions permitted to have no outputs (i.e. all inputs become transaction fee)?

I am interested in the possible use of the Bitcoin (or other altcoin) blockchain as a generalized distributed ledger, meaning that it is useful for tracking information other than coin transactions proper. A prerequisite for that would seem to be the ability to pay for transactions whose primary purpose is not moving Bitcoins from one address to another. So, can Bitcoin transactions list no outputs, thus leaving all inputs as a transaction fee reward for the miner?