Are you going to paint the bumper cover yourself or have a shop do it? Each of the several times we've had bumper covers painted or repainted, it was done with the bumper cover off the vehicle on a special stand that was made to hold them.
If you are going to have a shop paint the new bumper cover, it might not be worth doing the removal and installation yourself since it takes very little time to remove and replace the grill and bumper cover if it's done by a person with experience. I've only removed and reinstalled a couple of front bumper covers including the one on our Sienna and I'd bet I could remove the Sienna grill and bumper cover in less than 15 minutes by myself and reinstall it in slightly more time with a helper. A helper is useful to align the tabs where the cover meets the fender so you can "slap it" into place.
The plastic headlight lenses can be refinished to look like new as long as they're not broken. I've done it a number of times on other vehicles using a $20 to $25 refinishing kit purchased at an auto parts store. I paid a Toyota dealer around $75 IIRC to refinish the headlight lenses on our Sienna several years ago and the process they used seems to be holding up better than the kits I used.
I assume that the two brackets you mentioned are the ones that the headlights also attach to. I don't remember them being separate parts but it's been a few years since I did it. Here's a link a photo of our Sienna with the front bumper cover removed:
It seems a bit late to be doing this on our 2014 Sienna as we enter our forth winter with it but the past couple of days of driving in winter slush has pushed me over the edge. Stopping on long trips in darkness to wipe down headlight lenses with a wet rag in windy, below freezing conditions is...
www.siennachat.com
I think there's only three plastic clips holding the bumper cover on beneath the grill and one clip and one screw in each wheel well. The bumper cover is mainly held on by the 10mm bolts at the bottom of the cover. Here's a link to another photo showing the front of the bumper cover with the grill removed:
It seems a bit late to be doing this on our 2014 Sienna as we enter our forth winter with it but the past couple of days of driving in winter slush has pushed me over the edge. Stopping on long trips in darkness to wipe down headlight lenses with a wet rag in windy, below freezing conditions is...
www.siennachat.com
You're list looks complete to me. It's surprising how little is holding the bumper covers in place.
Also, line up the tabs on the ends of the bumper cover with the slots in the fenders BEFORE you screw in any bolts or other fasteners. I've found necessary to flex the bumper cover to get the tabs to pop into their slots which is about impossible if any of the fasteners have already been inserted.