Ahh ok, so the number really just defines the size of the hole in the board that the lens itself sits within. For the sake of ease, 'modern' LF lenses have a front cell (group of elements) and a rear cell, which screw into the front and back of the shutter unit, respectively. Typically modern lenses were sold with shutters, so that the aperture iris built into the shutter unit had a calibrated settings scale suited to the specific lens it had attached to it. Copal was a brand of shutter, as were Seiko and Compur (?) and the number refers to the size of the unit itself, and the corresponding size of the hole in the lens board that it sits within.
The terms people use are 'the lens' which typically refers to the collection of the front and rear cells and the shutter unit (which typically does contain the aperture as well). The lens board is what the lens sits within in order to marry it to the front standard of the camera itself. It is then simply a case that the lens board needs to have the hole in the middle that fits the corresponding shutter unit, and a overall shape that matches your specific camera. The most common shapes are Linhof style (which camera like Ebony, Shen Hao, Chamonix, Intrepid, Chroma etc accept natively), which are about 96x98mm and have clipped corners at the bottom, and Sinar, which are 140x140mm. Unless you plan on getting an 10x8 camera, or a Sinar camera, it's unlikely you'll need a lens mounted in a Sinar lensboard. Not to confuse things, but you can transplant lenses between lens board styles, provided the holes match. So for example, a lens mounted in a copal 0 sinar lens board can be simply moved onto a copal 0 linhof style board, and vice versa.
The standard Copal shutter sizes are 0, 1, and 3, and there are a few other less common sizes as well. The main thing though is that any lens you buy should come as a complete unit (lens cells, shutter and lens board. If this is complete, and the lens board is the right style, you're all sorted

If it doesn't come with a lens board, this is the easiest thing to fix, as one simply buys a suitable lens board for that shutter. In the beginning, perhaps stay clear of people selling 'lens cells only', as shutters are much harder to come by, and may not have an appropriate aperture scale for the cells you want to mount to it.
As for lenses that come without either a mechanical shutter or aperture, these are less common. Depending on what you shoot (portraits), I would not go for a lens without a shutter or aperture. Lenses without shutters are fine for long exposure (provided it comes with at least an aperture) as you can use 'top hat' timing - literally, use a top hat, or dark cloth to uncover and cover the lens. This is fine for exposures of tens of seconds or more, as the error in the precise timing is typically unnoticeable. Lenses that come without an aperture I would avoid personally.
Apologies, I know that's a lot to take in; do let me know if you want anything clarifying!