You have been given some good advise. a couple things that come to mind.
If you are going to hunt more buffalo and an occasional elephant the 450/400 is a great round. If you are going to hunt equal amounts of ele and buff get the 470.
I have owned most of the entry and mid level doubles and will throw in some experiences.
Owned two different sabattis. one shot well one didn't. Don't own either one any more.
Owned a Rizzini shot lights out but was a pound to two pounds to light. Don't own it any more
Owned a Siace and was one of the best doubles I have owned that was less than 10 K. It didn't fit me so I let a gent that it fit buy it. That is one I wish I had kept and takend a rasp to the stock and make it fit me.
Have owned 5 different Chapuis, all fit me and the fit and finish is very good and in my opinion the best of the under 16K doubles. I upgraded within their lines to the two I have now a RGEX and IPISHI.
Currently own a Krieghoff and love the rifle. IMO it is the best in the 16-20K range
Have owned a Hyem and Verney Carron both are great doubles. My Hyem was a older model 55 in 7x65 and the two VC are 8x57JRS and 450/400 (The 450/400 I never should have let go of.
These two brands are the best in the 20-32K range IMO.
I have never owned a Merkel but shot a few and I rank them above both the Sabatti and Rizzini.
As for reloading, it will save you money and allow shooting your double more, But with caution double are different to load for. Get Graeme Wright’s Shooting The British Double book and read it cover to cover several times before you start down the road of loading for doubles.
pay heed to
@rookhawk what he said IS SPOT ON!
Take you time and save a bit longer to get a quality double. It will save you some school of hard knocks experiences.
If you aren't positive of getting a quality double you would be better off buying a NICE bolt gun.