A flattener can be useful if you have the rigging for it available. I have no flattener currently and would like to have one back. However, the boats can be sailed fast without a flattener as well (saving the weight and complexity of the flattener system).

I have purchased dacron, kevlar, and carbon mains. Carbon is my preference, but many folks prefer dacron. As Jason mentions, carbon will keep its shape longer. Dacron is touted as more "forgiving" in wind & lumps, but I haven't found that feature to be that noticable.

Loose foot is best.

We've never used the window high in the main much. However, a window down low for seeing boats on opposite tacks (which I currently do not have) is a huge safety feature. Highly recommended.

I have a full top batten, which doesn't really hang up on the backstay if it is set up correctly (ie, correct tension, use soft batten in light air).

I've been buying Quantum sails. Lots of local sailmakers can provide a good sail and also good service. Having an ongoing relationship with a single sailmaker is beneficial.

--brendan