What are the different approaches to upgrading from a very old suitecrm version: 7.1.x that has lots of customizations to a more recent version 7.10.x
First, I will recommend you to create a backup of your SuiteCRM installation and your DB. Then create a test environment were you can test your upgrades.
I will start by upgrading to the next to mayor versions. For example I will try to upgrade to 7.3 to see if all works fine. If it does, then I will upgrade to 7.5 from 7.3…
You should keep into consideration that your custom code might need to be reviewed as well. If you use a custom theme, you will need to upgrade it to, to make sure it’s compatible with the version you upgrade.
Sometimes is good idea to disable your custom theme in order avoid issues during upgrades. I needed to disable it, specially after version 7.13
Thank you so much for your response. What would you recommend if I just create a new fresh installation of v.10.x and merge the database then resume working on the customizations one after the other?
It’s hard for me to recommend because I don’t know all the details related your installation. I think that’s a decision you will need to take based your needs. Now many questions can be responded by reading the post linked by @pgr