Give that the system appears to be a port of an existing MYSQL database it is unlikely that Views, Stored Procedures or Triggers will be an issue as there features were added in MYSQL 5. Views, Triggers and Stored Procs

Historically MYSQL databases have not tended to use Foreign Keys to the same degree as Oracle and other relational databases. Foreign keys only work with innoDB tables FOREIGN KEY Constraints

Subselects were added with MYSQL 4.1 SubQuery Support. I recently came across some historic code that attempted to get around this by creating temporary HEAP tables on the fly. :(

Grants may be an issue especially if you have any exotic code (like creation of temp tables).

Hope it helps
UnderMine