So I want to make a character that is a former veteran of some badass halfling squadron of Spider Riders, starting at level 4.
The spider he's using is a Giant Wolf Spider:
Medium beast, unaligned
Armor Class 13
Hit Points 11 (2d8 + 2)
Speed 40 ft., climb 40 ft.
STR 12 (+1), DEX 16 (+3), CON 13 (+1), INT3 (- 4), WIS 12 (+1), CHA4 (- 3)
Skills: Perception +3, Stealth +7
Senses: blind sight 10ft. , darkvision 60ft., passive Perception 13
Challenge 1/4 (50 XP)
Spider Climb: The spider can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.
Web Sense: While in contact with a web, the spider knows the exact location of any other creature in contact with the same web.
Web Walker: The spider ignores movement restrictions caused by webbing.
Bite: Melee Weapon Attack: +3 to hit, reach 5 ft., one creature. Hit: 4 (1d6 + 1) piercing damage, and the target must make a DC 11 Constitution saving throw, taking 7 (2d6) poison damage on a failed save, or half as much damage on a successful one. If the poison damage reduces the target to 0 hit points, the target is stable but poisoned for 1 hour, even after regaining hit points, and is paralyzed while poisoned in this way.
A halfling weights 1/3 of a standard humanoid, so the gear for him probably scales the same way, too. Even using the stricter variant rules on weight the spider can carry about 60 pounds without it slowing down, which means weight is not an issue for the spider to move at full speed. Assuming I have an exotic harness and skill with Animal Handling, what would I need to do in order to ride this spider upside-down in caves and whatnot?
And should I take Mounted Combatant for the sake of flavor? Unfortunately, the size ruling will not work with a medium creature very well, unless the GM decides to break that rule.