You can find all of these rules in the D&D 5E basic rules on Weapon Properties at
https://www.dndbeyond.com/sources/basic-rules/equipment#WeaponPropertiesIn short: yeah, loading means only one shot per round, and heavy is unfortunate for small creatures. However, once more feats are implemented, that will probably include Crossbow Expert, which removes the loading problem, allows you to attack with ranged weapons while in melee without disadvantage, and lets you make off-hand attacks with a hand-crossbow.
Normally, the main disadvantage of a short bow is range, but that's not implemented -- both longbow and short bow have the same range right now. So it's only a tiny difference in damage. (As a ranger, hunter's mark and other features amp up your damage so the weapon die size isn't a big deal.)
Dwarves are medium creatures rather than small, so not affected by the restriction on heavy weapons.