"You can Tribute Summon this card in face-up Attack Position by Tributing 1 "Steelswarm" monster" is not treated as an effect.[1]
If you Summon by the method "You can Tribute Summon this card in face-up Attack Position by Tributing 1 "Steelswarm" monster", it can only be Summoned in face-up Attack Position. (It cannot be Set.)[1]
If you Tribute Summon by the method "You can Tribute Summon this card in face-up Attack Position by Tributing 1 "Steelswarm" monster", you can also Tribute Summon by Tributing a face-down Defense Position "Steelswarm" monster.[1]
The monster effect "When this card is Tribute Summoned by Tributing a "Steelswarm" monster(s): You can target 1 card your opponent controls; send that target to the Graveyard and gain 1000 Life Points" is a Trigger Effect. (The effect targets 1 card on your opponent's field.)[1]
Applying "send that target to the Graveyard" and "gain 1000 Life Points" are treated as being done at the same time.
Since "Steelswarm Girastag" is a Level 7 monster, it normally requires 2 Tributes to Tribute Summon. When doing so, you can reduce the Tribute by 1 using the effect of "Amarylease". "Steelswarm Girastag" also allows you to Tribute Summon it by Tributing only 1 "Steelswarm" monster, but when doing so, it is not possible to further reduce the required Tributes using "Amarylease".[2]
If the effect of "Steelswarm Girastag" is activated while "Macro Cosmos" is applying, the targeted opponent's monster is banished instead of being sent to the Graveyard, but you do not gain LP.[3]
If "Phantom of Chaos" is treated as "Steelswarm Caucastag", "Steelswarm Girastag" can be Tribute Summoned by Tributing that 1 "Phantom of Chaos" using the method "You can Tribute Summon this card in face-up Attack Position by Tributing 1 "Steelswarm" monster", then you can activate the effect "When this card is Tribute Summoned by Tributing a "Steelswarm" monster(s): You can target 1 card your opponent controls; send that target to the Graveyard and gain 1000 Life Points" of "Steelswarm Girastag".[4]