I tried it importing exporting in order:
It worked pretty well but I had to replace into each view the ref_id to the images
where 87 is the id of the ir.attachment in the old website
where 1 is the id of the attachment in the new site.
I could not try, but maybe if I were to import ir.attachment before ir.ui.view i would not have need to manually replace them.
Next time I will try it :)
I also had to adjust parents in the menu items and I had to exclude from import the unknown fields.
Another issue is about the size of attachments: because of the size limit I received the error message during the import:
"Import preview failed due to: field larger than field limit (131072)."
I fixed it by using
(see https://www.odoo.com/forum/help-1/question/fixed-csv-product-import-issues-import-preview-failed-due-to-field-larger-than-field-limit-131072-57081 )