No, gmail isn't secure at all, im currently using my own server (most secure) and protonmail.ch (swiss company, promises to encode everything and nobody can view your mails without the Encryption Code)
Thumbs up for custom hosted e-mail ! You have the advantage of using your own @Domain which also looks professional to others and gives more trust. Security is also the best when your e-mails are hosted on your own managed server.
Solutions are available that allow end-to-end encryption with your current email account. CloudMask is one of them. It is easy to install and is a globally recognized security certification. CloudMask blocks the data as it goes to email service providers (GMail) and shields the data into random tokens whilst maintaining the complete functionality of the email application.