Mathamatica vs Sympy and Astropy to solve basic astronomy problems: solving linear equations and unit conversion
Unit conversion and handling is good in Astropy, if you need to convert astronomical units I recommend that you do use that package.
Regarding symbolic equations, SymPy is good, but you'd probably be better off doing theoretical work to figure out the units of the outcome and just plugging float numbers into Python. From my experience, having Python solve with units involved is time consuming (especially if you want a scalable solution).