This is a variant of Gate Order, aiming to swarm the field with high level normal monsters using special summoning tools like Secret Order and Parallel Birth Gate. Some builds also play Ancient Rules which we will not be using.
Generally the number of vanilla level 7s Gate Order uses ranges from 9-12, we're on 10 as that felt like a sweet spot for me, you can certainly experiment with what you feel is best. The specific level 7s we've chosen are all of the Galaxy targets: Galactica Oblivion, Milky Wave Neo and Cosmo Titan, as well as a 1 of Ultimate Flag Mech Tough Striker as the 10th level 7 and for occassional Apocalypse - Beast Gear World matchups.
Gate Order also generally plays between 0-6 level 4 or lower monsters, this is done to make it easier to empty your hand to fully resolve Parallel Birth Gate and to not clog the board. You can choose to run more than that, I wanted the space for other spells in the deck instead. Transamu Rainac is an emergency Gate target since it can summon any Normal Monster, and is a Galaxy Type Monster. Ozone Layer is another Galaxy monster that's run because of exactly that, but Ozone Layer is also a discard outlet in case you need to empty your hand for Gate. It also can protect leftover Galaxy monsters that you can't protect with Secret Order.
Now, the reason that the Galaxy typing is important. Galactica Force requires you to shuffle 3 Galaxy Type monsters from your grave into your deck to give a big pump to your Normal Galaxy board. This card can boost for insane numbers in the mirror match, and even in other matchups it's a up to 900 ATK boost to your board, which adds up to 2700 extra damage. Because it only boosts Normal Galaxy monsters it gives even more reasons to play the high level Galaxy monsters, and Transamu Rainac as well since that can get boosted too. The card felt good at 1 copy, but if you want to run more you can dig deeper into the low level Galaxy pool, Strange Traveler, Transamu Klein, Satellite Pegasus and Bright Sentinel are ones I'd consider. While some decks that run Dark Revelation occassionally run even less shuffle targets comparatively, it's more important that our spells don't clog ourselves, whereas the Spellcaster variants are completely fine sitting behind their in-theme Mirror Force for a couple turns. Another Galaxy payoff we're running is Meteor Charge, which more standard variants also run as it's a very good card. Makes for some very big damage pushes and is a good out to cards like Ecdysis Caliguleon and Master of Sevens Road, when those come up in the first place. It also really helps in closing out the game when your opponent is sitting behind 3 set monsters every turn. Transamu Rainac has even more niches in combination with this card as it's a legal low level target that can meet the requirements to get both the piercing and the position swap. As a result, in a pinch you can fire it off early on Rainac to unclog your spell/trap zones if need be. Ozone Layer can also do this but you won't get the position swapping part of the effect, though that doesn't matter if there's nothing you want to shift the position of.
6 draw spells in 3 Ship of Seven Treasures and 3 Heavenly Gift is very standard, helps you unbrick and dig through the deck to find your power spells. Heavenly Gift occassionally can be used to just discard your hand and not draw if you desperately need to make sure your Parallel Birth Gate goes off. Same with Ship, though you are forced to draw at least 1 card, you can at least choose to deny the 2nd draw if you need to. We're also on 5 backrow removal spells in 2 Ghost Cyclone and 3 Hammer Crush. I like having this abundance of backrow hate as there's a fair bit of strong interaction that you can get rid of, Dark Revelation, Imptailing Crisis, Mirror Force and Battle Demotion to name a few (Secret Order may protect from some of these, but Parallel Birth Gate does not). Even if it's not getting rid of a trap, getting rid of a strong spell is good also as it starves the opponent of options and resources anyway. I personally prefer Hammer Crush as you can use it while you still control monsters, and as such you can use them while having the tempo lead and control of the board to make sure you keep that advantage and is also an emergency discard outlet for Gate, though Ghost Cyclone is a higher value card in a vacuum, not making you discard a card to trigger and even drawing you a card in admittedly not particularly farfetched situations. Really comes down to preference overall. Magical Stone Excavation is crazy in a deck that aims to abuse multiple strong spells and empty their hand, so it's no wonder it's standard to run 3 copies. Tribute to the Doomed is a very interesting choice for the Legend card, I personally really wanted a proactive removal spell over a more reactive but higher value removal option like Mirror Force. This is also the reason why I'm not playing something like Vacua Annihilation, it's just a tad slow for me. It being proactive means that you can make aggressive pushes with it at your own leisure more often, and is also less likely to clog your backrow unlike a Trap like Mirror Force. Normally I like playing Judgment of the Rising Light in my Gate Order builds but ended up cutting it this time, so I was lacking the proactive removal that I usually had and felt the need to run at least 1 other form to use, and Tribute to the Doomed is a fine card. The discard cost again also can fuel your Parallel Birth Gate as well. Being on Tribute to the Doomed also means that in niche Maximum matchups it is even easier to kill them as compared to Judgment without Card Devastation (which alone is also really good for the Maximum matchup).
Overall, very solid variant of an established strategy. Feel free to experiment until you get a build you personally enjoy if you prefer running other cards, there's many options to choose from even outside of the ones I've already mentioned.