Always do the G, ALWAYS! You need to "G" all the things!
If it's merely a range toy or it's a rarer and more desirable model, I'd consider leaving the safety alone. But aside from that, I only by Berettas if they're a G model or will take the kit. Yeah, the original G models were superior to the current models that pretty much all use the conversion levers, but you get used to them and they can be shaved down and rounded off some if you really want to.
As for the TJIAB, I'd go with a 12# or 13#. Probably the 13# if you really want to make sure it'll pop everything, but most folks don't have any issue with the 12# from what I've read.
I'd run the stock trigger for starters. The only flat triggers I have right now are on my M&Ps, and while I do want to try them on my 92s and PX4s, it's a low-priority thing. The stock trigger works fine, so run it for a bit and see what you think.
For grips, I like the VZ UltraThins that come on the LTT guns. I've never tried a set of LOKs and want to change that, but again, fairly low on my list at the moment.
Whatever you do, that'll be a gorgeous Brig when you're done with it!