Can some one please explain the fixed interest securuties for me.

If I look at the the market I understand the coupon rate ( the interest rate when the bonds were issued?)

And the maturity date is the date you get your money back?

But the buy and sell I am not sure about. I assume that say for Hellaby Holdings the buy of 12.9 means I would get 12.9% interest on the money I invest,while the sell 12 means 12% interest?

Also if the coupon rate is 8.5% and I buy at 12% then if i buy a $100 worth then I acually get $141 worth of bonds? Is that correct?
So if i hold those bonds to maturity Hellaby will pay me out $141? And also pay me $12 interest per annum?

Lastly what is the minimum number/ value I have to buy? Do you buy them like shares 1000 or 5000...? or do you buy them in $1000 or $5000.

I look forward to an answer thanks.