Sure, but if I'm reading Spotrac correctly, this contract puts them at $149.550M. That's without deducting the $10M. It also doesn't include Maeda getting any incentives, Perez's buyout, a 26th player, the possibility of Chacin making the team, and any callups to fill IL stints.
I'm not sure where you are seeing $149 mil. I see $131.5 mil under Total Payroll:
Luxury tax payroll is a little higher at $139 mil, but that's likely irrelevant to the Twins. (It ignores the Donaldson deal being a backloaded, etc.) Spotrac seems a little hard to read for my taste too -- for example, I can't see where or how they are accounting for the Maeda cash.
I prefer Cot's Contracts as my source, and they have the Twins at $135.5 right now for 2020 -- they are assuming the $10 mil from the Dodgers is spread out evenly over Maeda's deal:
Edit to add: Cot's also notes the 26th roster spot, and Perez's buyout counts against fiscal year 2019 which is generally how MLB teams operate. You are correct that IL stints will increase this, but it will basically just be at league minimum salary prorated for IL days. Per Spotrac's IL days for 2019 Twins, that would have been less than $2 mil.