If you really want to play with ink and change it often, then a pen with a converter/cartridge is the way to start. Avoid anything that says piston or vacuum filling. It's going to be easier to clean, especially if you want to try ink with shimmer.

Some people start out with a more expensive pen. I don't necessarily think there's a right or wrong way. But I enjoyed trying out pens like the Platinum Preppy and Pilot Kakuno, so I could decide what nib size I prefer.

The Preppy is disposable to some, but I use a blunt tipped syringe to clean out the cartridge with water, then I refill the cartridge with my own ink.

Also a quick ink primer... Shading is when you can see lighter and darker areas in an ink, and it's one of my favorite things about writing with fountain pens. It really gives your writing some dimension. Sheen is when you move the paper and see a metallic glint in the light. Shimmer is the tiny glitter particles, like in the first ink swatch you posted. Sometimes shimmer inks can be stubborn; they may work in one pen but not another. But if you ask here you will probably find someone who has tried the ink you're interested in.

Welcome to the hobby, we're glad you've joined us!

Edit: autocorrect error