Differences: Money/decimals, rounding, case-sensitivity, equality comparisons differences, db/table locks mechanisms, memory/worker management, table/column naming conventions, null fields/columns effects on queries.

Mmm what else. I prefer postgres so I'm very excited about this. So many foot-guns will no longer haunt us like on MSSQL and less db/table locks to try solve (pessimistic vs optimistic locks). Oh and we are going to save a gross amount of money per year, as we will also be able to switch off a couple of Windows Server VM's in the process. These puppies are costing us a ton (I think about half of our infra bill are licenses...).

Just create a branch, spin up a test db and try to port a small feature. Its very easy in most cases. Debian + dotnet + postgres = dream team.

If you only use MSSQL as a datastore, it's not too bad. If you used all the other features (MSAS/SSIS/etc...), it is much harder. PG also isn't a panacea - you're trading one set of issues for another. The biggest upside is that it's much less expensive :)