QUsing hBP01-065〈Takanashi Kiara〉's bloom effect 'Let’s do this!!!!,' can you choose not to add a holomem found among the top 3 cards of the deck to your hand and archive all 3 cards?

AYes, you can.

QIf hBP01-121〈Kotori〉 is attached to your 1st holomem hBP01-065〈Takanashi Kiara〉 and you Bloom with a 1st holomem hBP01-066〈Takanashi Kiara〉, can you draw a card with hBP01-121〈Kotori〉's ability?

ANo, you cannot.
Bloom level up refers to blooming from debut to 1st holomem, or 1st holomem to 2nd holomem. Blooming into same level is not considered level up.

QCan hBP01-065〈Takanashi Kiara〉's bloom effect 'Let's do this!!!!' be resolved when the deck has 2 or less cards?

AYes, it is possible.
In that case, you will see fewer cards but subsequent effects are resolved normally.