I think I can help you out a little bit.
First the hang tags:
Yes, retailers are going to expect you to provide the hang tags. You can go ahead and get them printed up if you like, and later add bar coded stickers. Just simply leave room for the stickers on the hangtags.
I would suggest joining a group for your bar codes rather than buying them separately, even if you only have 4 designs right now. You will need a separate bar code for each size, style, and color. For example, you say you have 2 designs on black shirts. Well, for just 1 design on black you are going to need a separate bar code for each size of that design on black.
So if you have 4 sizes (s,m,l, xl), that's already 4 barcodes for that 1 design. It adds up pretty quickly, especially when single bar codes average about $50 per. You can join and get unlimited bar codes for about $700/year.
Secondly, the insurance:
I know the thread you are referring to. I think it's here:
Liability Insurance
I talked about the liability aspect of selling t-shirts. Liability insurance is very inexpensive. But there's no need to be scared, just go buy you some and keep your peace of mind!
The likelihood that you would ever be sued over a liability issue is very small, but in the event you are, the cost of the insurance is well worth it.