1) Set up all leading pages without anything special.
2) Deliberately insert any necessary blank-left-hand pages.
3) You set each page with numbers i, ii, iii, iv... as a
using the "Convert existing pages to title pages" and the "Place title pages at" with its "Page" set to its page number i.e. to 1, 2, 3, 4...
But take care to set the last of these differently (to reset the page numbers) i.e. with "Reset Page Numbering after title pages" to the first number of your main text i.e. to page 1.
4) Use right-click->Page (the the Page tab) to select the type of number e.g. i, ii or 1, 2
All the normal page numbers i.e. 1, 2, 3, 4... will change en masse to whatever you set any individual page to (because they are all linked together to the same type and are all sequential).
All the initial page numbers e.g. i, 11, 111, iv... will change en masse to whatever you set any of their individual page to because likewise they are all linked together i.e. all pages of type "Title Page" share the same number-type are all sequential too.
If you don't place blank pages yourself and the renumbering option (you can only renumber once) falls on a left page, then LO automatically inserts a "BLANK PAGE" at the left - but after exporting as .pdf, this is missing - so ya gotta insert a real blank page here yourself to make it stick after pdf export.