You're welcome gerardeen.
Some notes on what you've said:
It seems that Scribus can't quite handle its automatic frames properly. If you're having to make sure that you insert enough new pages before appending the text then that sounds more of a workaround than best practice. It seems to work but Scribus should handle things better. I'd say it was a bug but I wouldn't want to try and come up with a repeatable workflow that the developers could look at.
Having said that, thanks for posting your information for others to see. It will probably help people with the same problem so it's great that you took the time to document it.
I can understand why you're using Scribus now. I suggested word processing as, for "simple" stuff, WP is normally easier to handle for most people. However, if you need control of things like kerning then most WP software won't give you that functionality. So using Scribus, in this case, is a perfectly reasonable thing to do.
ASIDE: There have been quite a few requests for Scribus to export to ePublishing formats in the past but I can't see that happening any time soon. Scribus is a fixed-layout application - designed for print work - whereas ePub formats, as you will know, need to be "flowable" depending on screen size, font size, etc. (More like a responsive web page than a normal page layout.) The changes necessary for Scribus to be able to offer both worlds would be pretty huge and would need way more resources to design, implement and test than the Scribus team has at its disposal. Then again, maybe there's a kind millionaire out there who can sponsor a team of IT post-grads to do the work!
The process of stitching PDFs together is dependant on which software you use to do it and the choice of software is, in turn, dependant on which OS you're using. (Scribus can't do this.) For instance, Apple Preview does quite a reasonable job allowing you to drop PDFs into each other and drag pages around until you're happy but it's only available for OSX. Typing "pdf stitch" or "pdf merge" into a search engine will give you loads of possibilities and each will have its own way of working so I can't really give any instructions here.
Something you might need to watch out for is how whatever software you use handles things like colour profiles (if you use them). Some software just manipulates the PDF at a basic level - good enough for most display purposes - but they ignore some of the more complicated areas which can mean that the resultant document can't be printed properly on professional equipment. This could be a problem but, then again, it might not. It's just something you've got to keep an eye on.
One other bit of advice I can give here is to be wary of online PDF Merge services, especiallly those that are free. Some of these services have as part of their T&Cs a line that says something along the lines of "Any document submitted to this service becomes the property of such-and-such enterprises." which generally means that anything you send to them is no longer your property and you could get sued if you publish it. And they are also then free to sell your stuff for publication without needing your permission. Nasty, I know, but it's not an uncommon practice when you're dealing with "free" online services. On the other hand, I'm sure there are nice people out there that just offer their services out of the kindness of their heart and there's no problem using them. You've just got to find them.
Anyway, good luck with your continued use of Scribus. I'm sure you'll get used to it pretty quickly. It has its own little eccentricities but once you know what they are it soon becomes second nature going along with them.