My Gmail account has many emails. If I add another Gmail account to my phone, can I make the new Gmail primary and still use my apps
If you add an additional Google account, Android will ask you which account to use when there is ambiguity. From the main screen of most Google apps (including Play Store), you can tap the upper left corner of the app, and from the slideout menu touch your email address (which will be at the top of the slideout menu), and then choose another address associated with the fun to use the app as that account.