When writing this, I didn't care too much about parallel fifths or octaves, because many Baroque composers (Italian or otherwise) didn't either. Like I said, this piece was intentionally composed as a pastiche. (Your quote)
I'm well aware of the "inconsistencies" of some music from the time, but they are indeed quite rare. Composers from the time DID care about those kinds of things, even a fast, matter-of-fact writer as Vivaldi was. Honestly, I'd love for you to point some straight-out 8ves or 5th's in Vivaldi's concertos of the kind you have in some passages
(the series of 8ves between vl.1 and vla in the last movement, mss. 5-12, especially because repeated, seems a little off). But that's me!
I just think that dismissing the whole "5th's and 8ves" problem for music written (then or now) during the Baroque and Classical period, by saying "they all did it" it's simply not fair and quite inaccurate. Whether today anybody cares or not it's another matter - personal taste. But you should consider that when you see those things in Bach, Vivaldi or Haendel (who cared), they are either justified or at least debatable. The real mistakes or "slips of the pen" are extremely rare - and some are due to printing mistakes or sloppy copyists anyway, like in the case of D. Scarlatti. Furthermore, frequent parallel 5th's & 8ves are ALWAYS dead giveaways that the music is not original from the time (not your case)...or the composer was an amateur (like those noblemen who cultivated music as an hobby). In all of these years I never came across a case which wasn't either one or the other (including my "sins of youth").
Don't get me wrong, I do still enjoy your music very much, of course, and to be honest, I don't know if I could have spotted the above 8ves after just one hearing! (the only really doubtful and notable upon first hearing is the unison across measure 1 & 2 in the slow movement, between vls. and vla., but that's mostly because the parts ARE in brief imitation with each other and one thing - counterpoint and independent parts - would negate the other - free orchestral "effect" of which Vivaldi was an innovator...it could be easily fixed anyway).
And, by the way (you could forget my nagging remarks above) the finale is perfect! Like many of those miniature finales in Vivaldi "concerti di ripieno".