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impler.io
Powerful CSV & Excel Import experience for SaaS 🚀 Save months building data import experience from scratch 💰
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SurveyJS
Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
The data import solution can help!
You can check out https://impler.io/ it covers many of the features you mention and you can extend its functionality as well like converting first/last to fullname. Your problems related to edge cases, configuration, and support will be resolved automatically with it.
It's open source at https://github.com/implerhq/impler.io/
I'm a co-founder of it and if you create a feature request for something you want, I will happily cover it.