".... Maybe they will order some such ships from Russia. They can then just put mobile launchers on them like on this one......"
Good idea, to buy good second hand freight ships, not order new ones. And convert them. At fraction of cost of building specialist vessel or buy it. This way a fleet of tens or a hundred can be built up real quick.
"..... Not as effective as a real warship but it can carry quite a powerful stock of weapon to deal with lonely ships........"
Not if you have numerical superiority. And this can be achieved by converting existing ships. And how many ships do you know that can launch mini- Subs? Maybe 4 to 6 of them? Extend range of mini-subs, to cover choke points like Bab-el- Mandab or coast of South Africa to Antarctic? The subs can sit and listen for weeks , and get picked up later.
Iran needs to develop tech in all areas. Ability to build all equipment. Once technical knowhow achieved, then with Russia and China, all contracts can go to tender. The one with lower cost and good quality, gets picked. In open fair market. So it could be that a product gets built in three different places. A little like Euro fighter project.