I believe the point of Q1 is whether it makes sense to shift SA+OA funds into RA in order to earn higher interest (RA interest is higher than OA interest), and then to benefit from that higher interest in the form of higher CPF LIFE monthly payouts. The short answer is yes, that maneuver can often make a lot of sense, particularly when there are a lot of OA dollars relative to SA dollars, enough "headroom" to make the top up, and enough wealth/income to "bridge" at least to age 65 (the earliest CPF LIFE payout start age).
With respect to Q3, starting on a member's 55th birthday (when his/her Retirement Account is formed) it's possible to top up that new RA to the Enhanced Retirement Sum (ERS). It's then possible to make additional top ups every time the ERS is raised (every January 1st presumably), and only principal is counted for purposes of determining the maximum top up amount. A member who does this, who tops up to the ERS on his/her 55th birthday then every January thereafter as the ERS increases, will receive a higher CPF LIFE monthly payout than listed in CPF's sample ERS-level payout illustrations. Also, CPF illustrates projected payout amounts when starting payouts from age 65, but that's not actually the default. The default is that payouts will start at age 70, and those age 70 payouts amounts are substantially higher than CPF's age 65 illustrations.
Finally, one comment about the "highest payout." Yes, the CPF LIFE Standard Plan provides the highest nominal payout amounts initially. The CPF LIFE Escalating Plan provides progressively increasing monthly payouts designed to maintain steady purchasing power in the face of ~2%/year inflation. Members who simply live long enough (or longer) will see the highest nominal payout amounts from the Escalating Plan.