Right on, now that's a good deal.
1500mAh OEM battery should be awesome on your 3.7" and a good ROM can ensure you only charge once a day.
You can always do CM7 if you don't like the Sense ROM. That thread you linked has frequent posts, that's always a good thing.
I prefer tweaks and ROMS from XDA, in my experience they have more bugs ironed out compared to others. Key benefit of your phone is that as a new Android user, you don't have to do trial and error yourself when customizing, it's probably been done by others many times. because it's so popular. I'm grateful for XDA forums, reading and asking there saved me a lot of trial and error stress.
When you use Sense especially the 3.5 version, pay attention to RAM usage, it's known to be quite a resource hog. If you notice battery life is an issue, get the free current widget and log your power draw. It's one of the reasons I went with CM7, IMO, it's a more efficient and performance oriented.
Again, I must emphasize, read the XDA forums it will save you a lot of time tweaking the phone to your liking. Keep us updated on your progress.