Acuna is extremely unlikely to sign an extension taking him through his age 30 season, dropping him onto the FA market ahead of his age 31 season. His agent knows his skills are going to be richly rewarded in arbitration, so there is little reason to give the Braves a huge discount.
The Braves already control Acuna's age 21-26 seasons, and assuming the star/superstar path he is likely to take, the upper limit of his cost will be roughly...
2019 (21): $0.75M (pre-arb 2, similar to Bryant)
2020 (22): $1M (pre-arb 3, similar to Bryant)
2021 (23): $10M (arb 1, will flirt with Bryant's 1st year arb record)
2022 (24): $15M (arb 2)
2023 (25): $19M (arb 3)
2024 (26): $23M (arb 4, flirting with Donaldson's 4th year arb record)
That puts the upper bound of Acuna's earnings going year to year at around 6/70. He will then be in line to hit the open market ahead of his age 27 season poised to sign the largest contract in MLB history, and certainly larger than $400M, while making upwards of $40M per season.
So the Braves need to guarantee less than 6/70, while pushing a chunk of the money forward into his pre-arb seasons, and secure 1-2 options at around $30M to make sense.
Your proposed $2M/$4M/$10M/$13M/$16M/$19M comes out to 6/64, and is roughly in the ballpark, and may actually be a bit steep.
The 4/103 tacked onto the end is not realistic at all. Acuna is not going to give up his peak earning years that will see him earning $40M per year.
The most likely extension is something along the lines of 6/60 for his control years, followed by 1-2 options at $30M+. That allows the Braves to save ~$10M per year on a couple FA years, and still allows Acuna to hit the FA market in time for a record setting deal.
The most likely outcome is he does what all recent elite young players are doing and goes year to year so he can hit FA at the youngest age possible. The Braves knew this, which is why they correctly played the service time game with him.