As phone technology marches on, storage demands increase. It's now to the point that 8GB is kinda minimal. By the time the OS, legitimate software plus bloatware, etc is installed there's not much left sometimes.
Unfortunately, you've spent some time and effort doing some stuff that doesn't help much. For starters, install this simple little app called Storage Truth. It's very small and will install in very limited space. It will tell you how much space you actually have left for installing apps:
https://forums.androidcentral.com/e...pps/details?id=sa.storagetruth&token=P2V3_K17
Ok, regarding your problem...These are things that usually make little difference:
When you move apps to SD you cannot move entire apps. Part of the app must remain in /system for it to operate. Sometimes very little or none if an app can be moved. Also, pre-installed bloatware, any such apps which cannot be removed unless you root the phone, are installed in different space than apps installed from Play or other sources. So uninstalling those does nothing to increase space available for installing regular apps.
Contacts take up little space, a few MB even if you have hundreds with photos and lots of other info. And turning off contacts sync makes no difference in the space used, unless, I guess, you don't keep contacts on the phone, kept online only. That would be awkward...
I strongly, highly recommend syncing contacts to your Google account!
Clearing cache files is not a solution. It's the Fool's gold of making space. Fool's gold is not real gold and space made by clearing caches is not real space. It will only make space temporarily since cache files will rebuild over time. Also, while clearing cache files won't hurt anything, they're there to speed up operation and should be left alone.
That said, in this particular case I would empty the cache for your email app, but only the email app.
These are things that can help make significant additional space:
I think with every fairly recent email app I've ever seen, you can set limit on how much email is synced (downloaded) to the phone, either by date received or number of emails. Check this to see if it keeps email from certain people too long or an excessive number of emails.
To make space you can also:
Delete texts. If you have a LOT of texts, especially MMS, saved on the phone this can help.
Delete or move photos, videos, documents, etc to SD, cloud storage or a computer.
Uninstall app updates.
Uninstall apps you have downloaded and installed.