Do they buy beer kegs n how much

I don't think they buy kegs. You can trade your empty keg for a new one, plus the price of the beer. that saves you about 30 bucks.

Yes

1/2 a keg of bud lite is 129.99 plus deposit. It depends on what beer you get and the deposit amount. But yes they sell kegs.

Yes. It depends on the brand.

I'm sure you can & how much I wouldn't know...