The single biggest issue you're going to hit on the database side of things is the new cardinality estimation engine that was introduced with SQL Server 2014. The new CE is great for most queries, benign for some queries, and downright evil for a few queries. The best bet to deal with this is to use the Query Store. When you migrate your databases into 2017, enable the Query Store on them, but leave them in the old compatibility mode. They'll use the old CE and performance should be largely the same (not counting bigger/faster machines,etc.). Run your load for an appropriate period of time (day, week, month, you figure it out). Then, after that period, with the data gathered by the Query Store, change the compatibility mode. If you see query regressions, you can use plan forcing to make them use the old plan until you come up with a more permanent solution (which usually entails rewriting code).