I own a H16 and a Nacra 500,
Bouth are very fun and very good for the first steps in cat sailing.

The H16 is a very old design and the fact that there are plenty of cheap used parts is not always an advantage,
Those parts have been used by so many sailors so many years, that they are not useful any more.
I found my self fixing the boat 90% of the time and sailing it only 10% of the time.
Now the H16 is decorating my roof and is used mostly as a resting device for birds,

I say go with the Nacra
Add a spi

Take your time until you are ready for the real thing – A Blade F16