Mono blue Tempo - This is the legacy build. It usually starts with 4x Lord of Atlantis, 4x Master of the Pearl Trident, 4x Cursecatcher, 4x Silvergill adept. In legacy this is an Aether Vial deck to free up mana and make more use out of lands. Free counterspells provide the disruption to win against faster decks. In terms of the creatures, the main builds either stop at 2cmc and leave vial there, or add in Merrow Reejerey + True-Name Nemesis. Reejerey allows additional vial activations, and true-name is just insanely hard to deal with.
UG Aggro - This is the builds coming out of Ixalan block. I don't know a huge amount about these, but green allows for some super efficient beaters. This can probably be slightly faster than the mono blue tempo build, but losing the disruption will hurt.
Now we're getting to the slower strategies. From here on most of these decks should be including 4x Seahunter for consistency.
Millfolk - This is usually based on Drowner of Secrets and if including white, Summon the School. Merrow Commerce and Merrow reejerey provide additional activations, and there are enough bodies that Lullmage Mentor may be relevant. This is a slower casual strategy.
Wanderwine Prophets combo - Wanderwine Prophets, if made unblockable, closes out the game extremely fast. This deck would prefer to play Merfolk Sovereign over other lords for this reason. Resolving a seahunter + wanderwine prophet is usually game because the seahunter can tutor the merfolk for wanderwine to sacrifice.
Lullmage Mentor control - Lullmage Mentor is a strange card. Unlike other merfolk, it doesn't play well with tribal buffs or evasion. If you go in on this card, the deck is going to want token generation (Summon the School), and tons of control pieces. If you are running enough merfolk, Silvergill Adept and Deeproot waters will be excellent here.
Now for your deck. Without making an assumption about your overall strategy, I would say that Stormtide Leviathan and Archetype of Imagination are a waste. They aren't merfolk, and have extremely high mana costs without doing much that you couldn't do with your tribal cards.
Steambed Aquitects is also probably not worth running just because it's low impact. If you like Rootwater Matriarch, I would look into Seasinger. If I were to build a version of this I might try something like this:
With this design I'm really trying to play around seahunter. Cursecatcher is a threat at instant speed off of seahunter, and a number of key cards can drop in quantity because seahunter is available. Deeproot Waters plays nicely with Lullmage mentor. I'm not sure if this is enough to get mentor online, but some testing is required. Now for my, "I wish I could play this" build for lullmage.
I wish I could afford Nether Void