[brucepick]

Build a full belly pan first, while it's up higher. Easy to crawl under and attach your panels. Then lower it if you want. Make the panel easily removable (maybe stainless screws instead of rivets for example) to make undercarriage work reasonable to do.

I think you'll get more gain from the belly pan than from lowering - just a guess. But after you lower it building the belly pan is much more of a PITA.

Find the lowest part of what's underneath - probably the rear diff - and build the belly pan at that level. So the pan won't need to go up and down to clear stuff. Just cut it away where it needs to clear the suspension arms.

Grill block off - definitely a good idea. And faster/easier to do than lowering or belly pan, I would think. I strongly recommend a ScanGauge or any digital engine temp gauge so you will know the coolant temp. A needle gauge doesn't really tell you much. The engineers designed it with enough CYA so you can probably tow a big trailer across the desert with a/c running - but when you start modding it, their CYA design isn't there any more.