A few comments :
* ET also has a fleet of 30+ Dash 8-Q400s in service (their single largest type)
* ET doesn't have 9 737-700 and 17 737-800s as you have stated. There are currently just 3 737-700s and 7 737-800s in the passenger fleet - the remaining airframes are either with the subsidiaries (ASKY, Zambian, Malawi Airlines, etc..) or freighters.
* ET is supposed to take 3 more 737-8Max airframes by the end of 2023 (ET-BAI/BAL/BAN) taking that fleet up to 16.
* ET crews have full common type rating between the 777/787 so the same crew can fly the 777-200LR, 777-300ER, 787-8 and 787-9 interchangeably. This is partly why you tend to see a lot of last minute aircraft swaps between these types.
Finally, buried in the press release is the comment that Boeing will partner with Ethiopian for the refurbishment of their existing 787 fleet with new Business Class seats from Boeing JV partner Adient Aerospace (presumably their Ascent suite). This will begin with the older GE powered 787-8s that currently have the angled-flat Zodiac Aura Lite seats, and will be the 7th longhaul business class product that ET is operating. More interesting is that the Ascent seat is also certified for the 737 Max. ET has been pondering using the Max on some "third bank" routes into Europe and the major product dilution between wide and narrow bodies has been a reason they have been reluctant to do so. This is a possible way for them to get into this with a subfleet of Max.