hm, I could give you a best of list as such, the dsp limitation qualifier makes it a bit trickier.
in terms of unison preamp plugins, the neve preamp and century channel strip were made with the arrow in mind as far as I know. they both sound good, worthwhile especially now on sale.
reverb wise, I run a whole bunch of EMT140s on my Apollo 8 Quad, so it can’t be very taxing…and it sounds beautiful! It’s on sale right now, 99€.
delay wise, the Galaxy Space sounds good and is not so resource intensive.
i think the analog classic bundle which usually comes with the interface has a bunch of compressors that aren’t resource intensive, I like the Teletronix LA2-A on my vocal chains.
I wouldn’t bother with EQs unless you want to print your signal with the effects and even then…save the dsp and sculpt with an EQ after.
I also love the Manley Vari-Mu Compressor on the 2-Bus, but that one is a resource hog. Same with the Culture-Vulture, just hits the spot for me
One word of advice: never buy their plugins at full price. they have a sale on every quarter, christmas being the best and most extensive one, closely followed by their summer sales. and stay subscribed to their mailing list, even if it’s a bit of a pain, but they do occaisonally send through coupons on there. With every purchase you make you usually get a 25€ coupon towards your next purchase (they are time sensitive though), last year they even gave out 2x 25€ per purchase around black friday…so I went on a shopping spree then and bought all the cheap plugs to amass coupons, then went for the heavy hitters lol. In any case, enjoy, UAD’s stuff is awesome!