You want to select two steels that have similar heat-treatment requirements. Specifically, they harden at the same rate, and you won't end up over-tempering one part of the piece while under-tempering the other. However one steel needs to have a higher alloy content and thus will resist being etched.
I know that a lot of makers of pattern welded stuff use a combination of O-1 and 15N-20 which is basically 2% nickel high carbon steel. Both of these are known to be easy to forge and easy to heat treat.
200 is 99.5% pure nickel with some small alloy additions. It's my understanding that smiths who add nickel as a decorative touch, use pure nickel. So this would be a good choice. Nickel has properties similar to austentitic stainless. It can be strengthened by forging, but quenching has no effect on it. By itself it's fairly soft and quite malleable.
4xx and 5xx series nickel are commonly known as Monel metal. From what I've heard from my machinist friends it's truly nasty stuff to work with. I cant think of any reason to use it in a knife.
Nickel alloy 718 (aka inconel 718) is a high-strength "superalloy" designed for chemical processing equipment. Forging, welding, and heat treating it would be an absolute nightmare. Likewise for C-276
41xx steels are widely used in bicycle frames and aircraft parts. These are commonly called "chromoly". Not knife blade materials in the least. Their virtue is their excellent strength, superb impact toughness and very good weldability. They can also be heat treated to increase strength, but you'd only get into Rockwell B hardness.
EN47 is a common spring steel with 0.5%carbon 0.15% V and 1% Cr. As-quenched you'd get up to 55 HRC, it might be a good choice for decorative work or table cutlery.
Might also work for knife blades if you welded it with a larger proportion of something like 440C stainless that has a higher carbon content, giving better overall hardness.
Heat treatment is oil quench followed by 2 hrs@ 250C which would give you under 50HRC. That's a fairly straightforward treatment.
8620 is used for case-hardened parts like gears. It has a fairly modest carbon content. Not suitable for knife blades either.
As far as I know 6150 is almost ubiquitous for wrenches (and crankshafts as well.) It's very similar to EN47, but it has more manganese and twice as much vanadium. This would also be a good choice if you paired it with a steel that had a higher carbon content and thus higher hardness. Note it might end up being cold-short when forging. i wouldn't know.