The odds for building a winner is low, but the odds for building a mediocre boat in the first try is pretty high. Sorry for being negative, but I believe it is very true. Getting a well proportioned hull dont just happen, it takes a lot of work and study. E.g. how will you meet the minimum weight while making sure the boat is stiff and durable?

If you want to build a proven design like the Taipan or the Blade, why not get in touch with the designers and ask them what they think about a homebuilding foam project?
Building in foam is not harder than ply, I think (I have never buildt a hull in foam, but I have done some repairs and other foam projects). But the materials are expensive, or at least I think so. I would definately have done a cost estimate by looking at the online store here and e.g. raka.com for epoxy/glass. When you think your cost estimate is pretty complete, multiply by a factor of 2, or even better, Pi. Then you have the probable cost for a finished boat.
Do you have a place to work and store your materials+results? Is the place insured, and will your work be insured?
If your not finished by the time winter comes, will the workshop be heated and warmer than 15degC?
Do you really want to mess around with glass, foam and glue, or do you want to sail an F-16?
Do you have family/friends/significant others who might have problems with you spending a lot of time on a boatbuilding project?

Sorry for coming down hard on you, but these are questions you should ask yourself before starting. It is all with the best of intentions. I have done a few projects and in my experience you need positive answers to these questions before you consider building. As a first time builder, I would definately have bought a set of plans. There are so many structural issues and clever things you pick up with experience that the plans will definately be worth it.

If you do decide to build, it have some significant rewards. Personally, I prefer working with wood a lot more than foam/glass, but foam/glass might be significantly faster and have a higher resale value. Good luck with your decision making!