IT service provider (seeking on behalf of an association) association software

We are a small IT service provider based in southern Germany and are looking for association software and association management software for a cultural association (with approx. 600 members).

The software should meet the following requirements:

• Main functions
• Member management (individual/families)
• Membership fee collection/billing
• Form letters/mailings (GDPR-compliant with additional customer fields)
• Accounting (configurable, individual chart of accounts, double-entry bookkeeping)
• Donation management
• Desired functions -1
• Resource management among members (helper organization according to topics and dates for events; similar to course booking, hall booking)
• if possible with online self-service entry and circular emails
• Desired functions -2
• Event planning with calendar functions
• Preparation of print and web content (advertising material), publishing workflow via 2-3 roles
• If possible, with PDF or HTML export
• Editorial system for text and spreadsheet documents, capable of online collaboration (e.g., Nextcloud-based)
• Mailing lists (mail distribution m:n)
• Server-based, individually hosted (preferably not cloud-based)

Five to ten software workstations are planned. Work will be carried out in an MS Windows system environment. Both iOS and Android devices will be used as smartphones.