Hi Elli,
If the other information is fixed value or can be obtained from contact information, you can create an on-demand workflow targeting at Contact entity to achieve your request.

Here, for example, create a lead whose Topic and Company equal to the contact's Full Name and Company.

After saving and activating the workflow, it can be inserted into the customer journey with the workflow tile and used to create leads for the audience contacts.

If the other information you want is unable to be obtained from contact information or requires to be filled in manually by contacts, it is recommended to create a landing page marketing form.
Set the form as creating / updating leads only.

Then inserted it into a marketing email and send the email with customer journey.
After the contacts receive the email, fill and submit the form, the lead will be created or updated according to the lead matching strategy you set.
Please refer to the following documentation to know more about the creating of the marketing form.
Create a landing page (Dynamics 365 Marketing) | Microsoft Docs