2 gores was normal enough, but 3 and four gores were not uncommon - especially in later periods. For instance C11 Norman definitely had 4 gores.
By underarm gores I presume you mean Gussets? They are little shapes used to allow tighter fitting sleeves (hence saving fabric). No provenance but generally accepted.
Trimmings were there but not necessarily in the form that we use them in reenactment: Tablet weave is generally used for Viking/Early Norman etc. However, for substantial amounts of that time it would have been embroidery rather than tablet weave. The tablet weave is a means of showing the decoration rather than saying that it was always used. Of course I am not saying that tablet weave was never used.
Brendan



