Aven Tactician

“Bolster N” means “Choose a creature you control with the least toughness or tied for least toughness among creatures you control. Put N +1/+1 counters on that creature.”

Flying is an evasion ability.

A creature with flying can’t be blocked except by creatures with flying and/or reach. A creature with flying can block a creature with or without flying. (See rule 509, “Declare Blockers Step,” and rule 702.17, “Reach.”)

Multiple instances of flying on the same creature are redundant.