Yes, the 1" one piece Mark AR mount will work for this scope and is set at a height appropriate for an AR.
The eyepiece diameter of the Leupold VX-Freedom 1.5-4x20mm Rifle Scope is 1.56". I recommend using the Leupold Quick Release Weaver Style QRW2 Rings medium height set at the link below for that rifle.
https://www.opticsplanet.com/leupold-quick-release-weaver-style-qrw2-rings.html?_iv_tube-diameter=1-in&_iv_ring-height=medium
Yes it will. Leupold tests all of their rifle scopes to the same degree under the same shock tests. This will have no issue on a .450.
The Leupold RM Rimfire No Tap Ring Mount model 178116 at the link below will work with the 3/8" grooved receiver on that rifle. The medium height Leupold RM Rimfire No Tap Ring Mount should also provide enough clearance with the Leupold VX-Freedom 1.5-4x20mm Rifle Scope.
https://www.opticsplanet.com/leupold-22-rimfire-no-tap-ring-mounts.html?_iv_ring-height=3-sl-8-in
The total mounting space of the Leupold VX-Freedom 1.5-4x20mm Rifle Scope is 5.4". The overall length of the Leupold VX-Freedom 1.5-4x20mm Rifle Scope is 9.35".
The Leupold VX-Freedom 1.5-4x20mm Rifle Scope is a magnified LPVO. So it will not co-witness with an iron sight.
The Leupold VX-Freedom 1.5-4x20mm Rifle Scopes have a fixed parallax at 150 yards. So the Leupold VX-Freedom 1.5-4x20mm Rifle Scope parallax can not be adjusted to 50 yards.
To mount the Leupold VX-Freedom 1.5-4x20mm Rifle Scope to an AR I recommend using the 1 inch diameter American Defense Manufacturing AD-RECON Scope Mount. This mount can be found at the link below.
https://www.opticsplanet.com/american-defense-manufacturing-ad-recon-scope-mount.html?_iv_tube-diameter=1-in
The MOA Area 419 CZ457 Improved Scope Rail you need depends on how far you plan on shooting. If you are mounting this Leupold VX-Freedom 1.5-4x20mm Rifle Scope I would recommend using either a the 15 MOA Area 419 CZ457 Improved Scope Rail. It can be found at the link below.
https://www.opticsplanet.com/area-419-cz457-improved-scope-rail.html
To mount the Leupold VX-Freedom 1.5-4x20mm Riflescope to a Marlin 1894 and the EGW rail, I would use these Leupold Backcountry Cross-Slot Low Rings.
https://www.opticsplanet.com/leupold-backcountry-cross-slot-30mm-rings-med-matte.html?_iv_code=LU-RR-MED-175116