If I'm reading this corrrectly, you've got a few problems here. Creating an invoice with FMP is easy enough, and with the greater control, a nice improvement over Bento. Why was the import a problem? Are you using the Starting Point solution from RCC? Have you contacted them for assistance? There shouldn't be any problem saving the modifications and there is a prompt from FileMaker Pro that you can default to always save. As to the iPad layout, I recommend looking at the iOS Resources tab here, and take a look at the templates created by FileMaker and Soliant, as they provide some good layout information.
Hopefully this is of some help. If you have some additional particulars, I'd be happy to take a look and see what I can do to help. The FMP community is pretty good and I'm sure you'll get your answers.
For your first paragraph There are Auto-Enter and calculation functions.
You can have the Data created Auto-entered (whenever a project is created), which you can change or leave it as a data field.
For the number of days worked you can have the field as a calculation where all you would have to do is date1-date2, ex. (Date_Ended_Project - Date_Created).
If you don't want it as a calculation field you can have a script trigger to run on the Date_Ended field.
If you need help with any of that let me know.
As for the other thing I'm not sure how Bento works. I do know that in FM you have to be specific on the layout size for an iOs devices.
Hello and welcome! You might want to take a look at our online video tutorials. Also note at the bottom of that page there is also a link to download our free FileMaker Go starter solutions, which may help with your mobile development. When you're ready to dive deeper, you may want to consider taking advantage of our promo for new TechNet members that gets you the FileMaker Training Series documentation for US$9.99 (normally US$99.00). HTH.