Don't know what the local conditions are there,so 2 km really depends on conditions.
I've had 4 people in a 10' inflatable 8 miles offshore in good weather, and been in a 38' a quarter mile offshore when I shouldn't have in bad weather.
You need to gauge the build by YOUR local weather& sea conditions, and operate prudently according to the current conditions.
I just looked at both those designs, and I feel depending on conditions, either would work for what you described.
They both have a nice deeper V bottom to them which is a better choice for rougher water than a lot of the lake & river boats on here.
The La Paz would be better for offshore in my opinion, and not that much more work.
I think you have a good idea though to get your feet wet on a smaller project first if you have some doubts....maybe a 11'Utility
https://www.boatdesigns.com/products.asp?dept=371This has higher sides and more room for your size, can re-space the frames closer together by an inch or two each to get you under the size limit, and is very similar to the techniques and methods you would use to build those larger ones.Plus it would be a great little inshore boat
hope this helps some.
Warren