Need some help finding rims. 1965 mustang 4 lug

So i got a front disk brake conversion kit from CSRP a while back and now want to convert it. Its a 4 lug and came with all the other stuff from their kit. I was told the original rims would not fit with this, that I would need a 15 inch. My questions are What wheels, and where can I find them. Apparently the bolt pattern on the rotor is 4x4.5. I was told maybe a 15x6 or 15x8 would be fine. Second question is do I need to change the rear tires aswell? Just tryna fix my dad’s mustang that he left me💯 thank you