NW,
You have been given good suggestions: 6 BR, 6 Dasher, 6 BRA, 6GT, 6XC, 6.5x47 Lapua.
All of these cartridges will work wonderful from 600 to 1000 yards.
The 6 BR, 6GT, 6XC, and 6.5x47 Lapua are not wildcats, so there is no fireforming to be done, which makes things easier for a new reloader. Throat/barrel life is good with all of these cartridges.
None of these have heavy recoil which will make in enjoyable for both of you.
A 1-8 twist barrel will work great for all of these cartridges.
Brux Blake, Bartlein, Krieger, Hart, and Lilja are barrels that I use, and will give you top performance.
Are you going to use a stock, that would use a front rest and rear bags?
If so, I can give you more recommendations.
There are many good actions, out there but a great buy for the money is Kauger Arms. It has a Remington 700 footprint.
I agree with the above. 6mm or .243 diameter is easy to shoot hundreds of rounds a day for both men and women because of the light recoil. From all my research I came up with using a round with more Horse Power and great barrel life. The 6XC beats up on the smaller cases types. I'm also a .243 win person. Very available no matter where you go. Read up on these