Still in what regards building a boat in steel or aluminium I believe the only disadvantage would be the less technological build in steel. Not that in aluminium is a lot more dificult but it is more specialized and as you pointed out, even if today electrolysis problems with aluminium are completely sorted out in professional boa building, that can be a problem with a more amateurish construction if they don't know what they are doing.
Since you have to build the boat in Brazil I would stop by now and I would go looking for aluminium professional boat building in Brazil (I am sure that there is shipyards), see if there is any at a convenient distance from where you live and depending on their quality and skill I would then go on regarding the material and type of project:There are several levels of difficulty in what regards stock projects: some are very easy, designed to be built by amateurs, others are better boats but only suited to be built by professionals.
I think that regarding your budget the idea of having a stock plan and then a NA or a Naval engineer to direct the building team makes a lot of sense.
Regarding the NA and the project I would regard as very convenient one that could take care for you of all cutting (computer assisted plasma cutting) of metal parts in a way that you would only have to assemble the boat in Brazil.
For instance this Swedish shipyard designs the boats, cut the parts and send everything to Poland where they assemble the boat. Just give it as example because they have a nice picture i can post but any NA with experience in 3D design with the right tools and used to work in metal can do this:
"Every single element in the construction of the VK series of aluminum performance sailing yachts is designed down to the last detail. The construction elements are then grouped according to their thickness and type of aluminum alloy. Each group is nested on plate forms that will be used for cutting by CNC laser and/or plasma cutters.
From the above procedure a construction kit is developed that is ready to go to the production. For the assembly of the construction kit, the sequence and the type of welding a special construction manual is made by VK Yacht to be used at the yard.
The metal used in the construction of the VK series aluminum performance sailing yachts are Lloyd's 3.2 approved aluminum alloys:
AL 5083-H32 for the internals (AlMg4.5Mn)
AL 5083-H0 for the plating (AlMg4.5Mn)
AL 6082-T6 for bars (AlMgSi1)
The production yard of the VK series of aluminum performance sailing yachts is in Gdansk, Poland. The yard had a long practicing experience in aluminum marine constructions already before starting collaboration with VK Yacht.
In the yard, prior to the assembly of the construction kit, the elements that need to be curved are formed with specialized roller machines. The final assembly and welding is performed by approved and well experienced technicians.
The total construction is supervised and approved by Classification Authority."
VK Yacht AB - Construction
Off course even if already cut in this case it is a project to be executed by skilled professionals and that's why I said that first I would look at what you have available as work force and then i would chose the material and the type of process.
Probably the Dutch have the better designers and specialized shipyards in what regards Aluminium Yachts, closed followed by the French, but in what regards simpler projects designed for the amateur boat building (easier to build) and overall less expensive boats, than the France is the place to look.
I can give you some suggestions, but first look at what you have available in what regards boat building.