Any suggestions about what part of the game to start adding enchantments to weapons or armor?  Like what level or guidelines on what weapons to wait for?  I don't require to be optimal but then I also don't want to waste materials...

Thanks!

You should put a lash on your weapon asap. It doesn't cost much but has a big impact. 

Enchanting your equipment up to exceptional is never bad - generally speaking.

What's a lash? Additional elemental damage e.g. Fire lash on Durance's staff?

Yes

One thing I didn't realize until doing some reading is that you can enchant something with 'fine' and then later upgrade it to a better enchantment (eg superb or excellent or what have you).  You don't get the materials and copper recycled from the 'fine' enchantment but it is nice to get a smoother start and put fine on weapons that don't come with that type of enchantment when you find them.

Oops, I didn't realize that that might be unclear. Yes, you can upgrade the quality enchtantments. Also Damaging II with Exceptional and so on. 

But while you can replace quality enchatments with better quality you can't really revert enchantments in general. E.g. if you put a burning lash on a weapon it will always stay there.