Q1: After this Digimon gets +3000 DP from the When Attacking effect, its Armor Purge activates. What happens to the +3000 DP?
The effect has already been activated, so the +3000 DP effect persists for the turn.
Lv.4 Flamedramon BT8-012 R Armor Form | Free | Dragonkin <Armor Purge> (When this Digimon would be deleted, you may trash the top card of this Digimon to prevent that deletion.)[When Attacking] This Digimon gets +3000 DP for the turn.
Lv.4 Flamedramon BT8-012 R Armor Form | Free | Dragonkin Digivolve: 2 from [Veemon].<Armor Purge> (When this Digimon would be deleted, you may trash the top card of this Digimon to prevent that deletion.)[When Attacking] This Digimon gets +3000 DP for the turn.
Lv.4 Flamedramon BT8-012 R Armor Form | Free | Dragonkin [Digivolve] [Veemon]: Cost 2 <Armor Purge> [When Attacking] This Digimon gets +3000 DP for the turn.
Lv.4 フレイドラモン BT8-012 R アーマー体 | フリー | 竜人型 「ブイモン」から2≪アーマー解除≫(このデジモンが消滅するとき、このデジモンに重ねられているカードを上から1枚破棄することで、消滅しない)【アタック時】このターンの間、このデジモンをDP+3000。