How do I isolate calcium from calcium carbonate?
The answer is you cannot do it almost for sure.

To obtain $\ce{Ca}$ metal from $\ce{Ca (+II)}$, you need to perform a reduction process. For this purpose, you would need a very strong reducing agent, because calcium is very close to the bottom in the Ellingham diagram (used in metallurgy for this same purpose: obtain metals from its salts).

So you will need to perform an electrolysis of molten calcium chloride, which is not cheap, and by any reason not doable at home or at an standard lab (just a quick view of calcium salts melting point will give you a hint about why is this...)