I was thinking tar remover and a stiff brush, maybe panel wipe to get any bits I missed, any other ideas?

After its cleaned, what is good to treat any rust patches? I heard hammerite kills rust, is this right? Im only giving it a clean and black waxoyl for now, and will do a proper spray + powdercoat jobbie in the winter, just want the car tidy for summer (central day is the target)

Ta for any tips