Code Search is a brilliant feature based off Elastic Search. I wanted to summarise a few tips from my relatively limited experience with Search Server for TFS 2017, which adds Code Search to your instance.
The first thing to remember is that the size of the index can be quite large (up to 30% the size of a collection in the worst case) so plan for it in advance.
CPU and RAM should not be underestimated as well. Elastic Search can be a quite intensive process.
If you are not an expert on it (like me 
The indexing process can be quite tough on the TFS scheduler, so bear in mind this when you install it – otherwise you will see some jobs delayed.
This should not have an impact on the users (all the core jobs have higher priority anyway), but it is worth remembering that the indexing job will have a similar priority to the reporting jobs, so there is a risk of slowing reporting down.