you don't need your wacom size to match your screen size
you don't need your wacom size to match your paper size unless you trace paper
for 24/27“ dual screen setup: medium size is best, small size will fly mouse too quickly but usable as mouse
for 24” screen: if you use medium size, you will feel very slow to move like mouse, but ok for drawing details, single small size will feel more balance between as mouse and drawing.
any screen smaller than 24“, just use small wacom is enough.
large size is not recommended to use as a mouse, your arm will feel tired to move from screen corner to corner.
compared with wacom screen version, tablet version works more like mouse and pen, while screen mainly use like pen input, with your hands on screen all the time.
compared to the lower line models, like bamboo and non-pro lines, they are more portable to use with travel laptop or as cheap alternative, but the pen is too slim for long time work use; and buy 2nd hand old gen wacom will be much cheaper and better to buy new cheap versions.
wacom tablet can use for more than 10+ years, if you take care the draw surface, put cover when not use.
(my old bamboo fun medium has served me well for at least 16 years, I gave it up later due to its sensitive sensor aged and behaved a bit shaky when in idle. also, I got cheap 2nd hand pro version wacom to replace it.)