Let me ask some questions.
Why are you applying Interprotect 2000? Does your boat have blisters or some other problem? IF it's an older boat and has never had blisters, you probably don't need to apply Interprotect 2000 at all. (If you're going to strip the boat to the bare fiberglass, it's not a bad idea to apply it, but it would really be a precaution against a possible future problem, and not a remedy for an existing problem.)
How do you intend to use your boat? Casual club racing? Serious racing? Cruising? If you intend to use it for serious racing, then no amount of work will be too much. If you intend to use it for club racing, then the surface of the bottom and keel should be smooth, but they don't have to be perfect. If you're a cruiser, you might be satisfied with even less perfection.
As far as I can tell from the photo, it looks satisfactory for club racing or cruising. You can put a couple coats of good antifouling paint on it and go sailing. If you sail it well, you should be able to win some awards with it. If you want to race seriously, then finish stripping it to the bare fiberglass, fair the keel, and apply good racing paint.
I wouldn't suggest that you make a bigger job of it than is necessary for you to enjoy using the boat as you intend to use it.
I suggest a good quality ablative paint. It's expensive, but I have used it for club racing and have been competitive. If you only give it 2 coats to begin with and one coat per year thereafter, as I do, it doesn't accumulate, and you should never have to strip the bottom of the boat again. It makes annual bottom prep easy.
I was thinking about putting on Interprotect as the Interlux site sort of scares you away from doing anything else. Heck, I was initially thinking of just sanding off as much of the old paint as possible and rolling on VC-17. Hmm, maybe I am overthinking this a bit too much. The boat has no blisters, the hull is smooth as can be, just a few too many layers of hard bottom paint on it to get right down to the glass. Interlux makes it seem that VC-17 will not stick to anything other than 100 layers of Interprotect or VC Tar (Just kidding about the 100 layers, but you get my point).
I intend to use the boat for club racing initially, but I would like to race competitively in the next year or two. There is an active Shark 24 group in my area and I would liek to race with them eventually. Well, Sailormon, you are making me think and I should just realize that slapping on a few layers of VC-17 as is couldn't really hurt anything. Heck, I could probably fair up the few imperfections on the keel (really nothing to speak of) and sail it as is!
Okay, time to realize it is a 48 year old project boat, and that I have years to get her perfect! I guess I will just sand her as smooth as possible, splash on some VC-17, and be done with it.
Now for Painting the deck, painting the topsides, replacing the bulkheads, replacing all the hardware....