I think it would take a hell of a lot of paint to fill in panel lines. Its been a while since I had a Heller kit, and I can't recall what they are like.
Give all that and these are your first (of many) 72nd kits, I don't think I would throw loads of dosh on the rear gun. Looking at the undercarriage, it does look like a pretty basic kit, and you could just go silly spending loads on it. But its a great build to hone your painting and weathering on, and your doing a great job on it.