Go with arm warmers and a vest. I remember this stuff being expensive when I started riding more in more varied weather and only buying things that were very very versatile. Over the years, through gifts and hand-me-downs, I have some long sleeve jerseys and such and on a long ride where either my effort or the temperature rises, I wish I only had armwarmers to slide down to cool off a bit instead of being stuck with the long sleeve jersey. After the armwarmers and vest, get a good cycling windbreaker. Then knee warmers.
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I don't do: disks, tubeless, e-shifting, or bead head nymphs.