Hi @Wolfgang,
Adding attachments and custom templates are in our priority list and will work on them as soon as we release Portable version( Cross-platform), Improved password generator on all platforms, Autofill on Android using notifications and improved Enpass keyboard, improved UWP with TOTP and one surprise feature for you. You can expect Beta versions of specified features in May itself and after their final release, we will work on Attachments and custom templates.
Meanwhile instead of custom templates, you can take help of Duplicate feature to create copies of your customized items.