Halt taking honey in his coffee. The other three recurring Rangers (Will, Gilan and Crowley) make it clear that it's considered incredibly weird, and nobody else does it. But Halt having a private sweet tooth makes sense. He grew up as the crown prince of Clonmel. So, unlike the other protagonists, he would have grown up having sweets on a near daily basis. He's more used to sugar than the other rangers. What's unpleasantly sweet to them is probably delicious for Halt. That's just how his palate developed.
Furthermore, lots of nobles practice archery when they're young. No wonder he's already an expert shot by the prequels-he's probably been practicing since well before he met Pritchard, who just "tightened up his technique."
Horace's knighting is a much bigger deal than may be immediately apparent to the modern reader. In our world, squires were usually knighted by the knight they served under, meaning that an Araulen apprentice would presumably be knighted by the Battlemaster or one of the Battleschool instructors. Getting knighted by the king is, in and of itself, a huge honour, let alone the fact that he's being knighted early and assigned to the Royal Guard.
On top of that, it also makes sense that he gets the early knighting and promotion, especially compared to Will. Not only does Will have more skills to learn than Horace does (map-reading, navigation, tracking, archery, knife-throwing, hand-to-hand, and drinking coffee with honey), Will spent the past year traveling with the Skandians, being enslaved, and then recovering. Other than keeping himself in shape physically on Skorghjil, he barely did anything to advance his training, and had to re-learn his archery and knife skills at Hallasholm and work to get himself back into shape. Horace, on the other hand, spent the past year training in Battleschool, traveling with Halt across Gallica and fighting the brigands there, then training with the Skandians before the battle. And before that, he had advanced training from Gilan, an acknowledged Master Swordsman in Book 2! In light of all that, Horace's knighting is much less surprising. And his promotion to Royal Guard? Well, perhaps Duncan was a bit of a Shipper on Deck for Horace/Cassandra even then.
In Book 12, Halt brutally condemns Will for wanting to focus on finding Alyss' killer over his orders from the top, despite having done the very same thing in Book 3, and when the country was in much greater need of all hands on deck. On the other hand, Halt ensured that someone would take over his responsibilities instead of just ignoring the country's need entirely, and his mission was also to benefit Araulen by bringing back a highly-talented Ranger apprentice.
In Book 7, when Selethen forgets to take Cassandra's seal to the Wakir and she has to remind him, it's actually a subtle bit of foreshadowing: Since he is the Wakir, he doesn't have to take it anywhere.
Book 9 has Horace accuse Halt of being in Master Chubb's kitchen not to appraise Will as potential Ranger material, but actually just seeing him by accident as he planned to steal his pies. Given the debt he felt to Will's parents (as expounded upon in Book 11), it's entirely possible that Halt was there to keep an eye on Will (and also to steal some pies while he was at it).