Okay - first off the shark in those photos is a Blacktip (Carcharhinus limbatus).
Second - it's a myth that all sharks need to move constantly in order to breath. The vast majority of species can actually be stationary and still breath normally. Only species which are ORV (Obligated Ram Ventilators) are required to constantly move in order to pump water over their gills. Those sharks tend be Requiem Sharks(like Sharpnose, Blacktips, Bulls, Tigers), Hammerheads, & Mackerel Sharks (Great White, Mako & Salmon Sharks).
Third - Benthic species - are bottom-dwelling non-ORV species. they breath by pumping water over their gills. Such species include Bullheads (Horn & Port Jackson Sharks), Catsharks, Nurse Sharks, Carpet sharks(Wobbegongs, Bamboos, Epualettes). Active level usually various depending on the exact family - but most get more active at feeding time.
As for active swimming species that mature at 3-4 feet.
Most available Smoothhounds - mature at 2.5-3ft, and max out at 4-5 feet.
Atlantic Sharpnose - mature at 2.5-2.9 feet, average about 39-42" in length, and max out at 4 feet.
Bonnetheads - mature at about 2.5-3 feet, average about 4 feet, and max out at about 5 feet.
While Blacktip Reef & Whitetip Reef Sharks tend to mature at 3-3.5 ft, they average 5 feet, and max out at about 6 feet.
As for Blacknose and "Mini-bulls" - Both species difficult species for a private aquarist to keep. Blacknose(C. acro although they max out at 5-6 feet - they tend to be tempermental. Mini-Bulls aka Finetooth(C. isodon) are roughly the same size as a Blacktip Reef, and have some difficult in acclimation to captivity. Also it should be noted that IMPO - Blacktip Reefs are a much better shark for a private aquarist than either of these species.
Before you settle on actual plans for the lagoon or on a specific list of species - may highly suggest that you first research(online) those species you've list, in most cases you have fine some useful information.