Store contacts locally?

I am in the process of moving to a Windows 10 machine after a decade in MacOS. After much searching and trial and error, I have found eM Client to best meet my mail and calendar needs and usage. However, the Contacts within eM Client have been massively frustrating to me. I had been storing my contacts in Apple’s Address Book in a local folder, and syncing it manually with my phone. I prefer this not only because it is my known method, but also so that I have a consistent list of contacts rather than lots of little contact lists in various email servers. I have imported my contacts list from my Mac machine, and I have allowed eM Client to access whatever contacts list my email apps had put together (without any manipulation or input from me). I have run the deduplicate process on them. I a) still have lots of duplicates with no way to merge them manually, and b) struggle to navigate my new contact list, in which I store not only email addresses, but phone numbers, birthdays, etc. I would like to have one centralized contact list where I can store all of this rather than having to update multiple lists, but I’m not sure that eM Client can really handle a general-use contact list, rather than simply an email address repository. Has anyone else struggled with this and found a solution?

See my reply to your Deduplicator question for your first question.

To store your contacts locally, you want to save them to Local Folders. If you can’t see the Local Folders, you can enable them in Menu > Tools > Settings > General > Show Local Folders. They will not be synced with your phone.

But wherever you decide to store them, you certainly can save all the data you mentioned. I have many contacts synced from my phone that have only a name and a phone number. I think that the only required field is the name or company. All other fields are optional.