Protein-ligand simulation gromacs 20.04

GROMACS version: 20.04
GROMACS modification: Yes/No

Here post your question… I successfully performed protein-ligand tutorial MD simulation. Now i am going to start my protein and ligand for MD simultaion, i wanna ask either i use protein and ligand structure separetely or separate my ligand from Protein-ligand complex?

qno2: Which and on what basis should i choose my forcefield parameters?