On jumping, I'm going to quote directly from the 5e PHB, of which I have a dead-tree copy (and note that some liberties, specifically concerning run-up, probably had to be taken due to how the game (and really any point and click game) handles movement). Emphasis theirs, typos mine:
Originally Posted by "5th Edition Player's Handbook, page 182"
Your strength determines how far you can jump
Long Jump. When you make a long jump, you cover a number of feet up to your strength score if you move ten feet on foot immediately before the jump. When you make a standing jump, you can only leap half that distance. Either way, each foot you clear on the jump costs a foot of movement.
This rule assumes that the height of the jump doesn't matter, such as a jump across a stream or chasm. At your DM's option, you must succeed on a DC 10 Strength (Athletics) check to clear a low obstacle (no taller than a quarter of the jump's distance), such as a hedge or low wall. Otherwise you hit it.
When you land in difficult terrain, you must succeed on a DC 10 Dexterity (Acrobatics) check to land on your feet, Otherwise, you land prone.
High Jump. When you make a high jump, you leap into the air a number of feet equal to 3 + your Strength modifier (minimum of 0 feet) if you move at least 10 feet on foot immediately before the jump. When you make a standing high jump, you can jump only half that distance. Either way, each foot you clear on the jump costs a foot of movement. In some circumstances, your DM might allow you to make a Strength (Athletics) check to jump higher than you normally can.
You can extend your arms half your height above yourself during the jump. Thus you can reach above you a distance equal to the height of the jump plus 1 1/2 times your height.
Basically, there are no rules concerning weight in jumping, and, horizontally, at least, even a basic character has superhuman jumping skills, if Larian stays true to 5e (though, unless everyone is less than 2 1/2 feet tall, you shouldn't be able to jump over enemies, per RAW and I'm fine with that). This is to keep everyone on the same page. I'm not sure how it translates in-game, without some way to measure jumped distance, but...
As to shoving, yeah, it should take a regular action, instead of a bonus action, again, per RAW.
As a side note, there are no rules about height difference (terrain-wise) in the PHB, so I guess Larian is on its own there. I wouldn't mind the advantage/disadvantage being turned way down and limited to accuracy, but I feel there should be a difference between being several feet above your enemy and several feet below.
In my opinion, the 5e rules concerning jump distance are not so bad, jumping 10 ft/3m (Strength score of 10) doesn't seem excessive or superhuman to me (when you run 10 ft/3m before the jump). And it would be easy to translate in-game, they already measure the distance you can walk.
Regarding the height difference of two combatants using ranged weapons: when I have a clear view on my target (no cover), it does not matter in my opinion if the target is a above me, on the same heigt level, or below me. But when I look up a cliff and see only the head of my enemy (or the upper half of the body), while he has a clear view on me, than yes, he will have some sort of advantage relative to me. I am at disadvantage, because part of his body is covered by the cliff. So we don't need rules concerning height difference, but rules for cover - and these are already in the 5e rules.
I know, Larian can't do this because of the Devinity engine, so that's why they came up with their current advantage/disadvantage system. Which is too excessive/too much in my opinion.
But all this was already written in these forums by many, many people.