Upgrading Meraki MR16 to 21.02

I've just installed 18.06.2 on a MR16 and would now like to upgrade to 21.02. I've read the advice at https://openwrt.org/toh/meraki/mr16 regarding the complexities of moving from ar71xx to ath79 which appears to offer three upgrade methods. I have a couple of questions:

  1. I have serial access - does this mean I can upgrade by simply following method #1 (listed as "ath79 (OpenWrt Snapshot and 20 onwards)" ?
  2. If I have another MR16 running stock firmware - is there a way to go directly to 21.02 and avoid this intermediate step ? The Tomesh guide simply references 18.06.2
  3. Is it possible to upgrade to 21.02 but stay on ar71xx ? How would this be accomplished and presumably this isn't recommended ?

Many thanks in advance