It varies.
In soccer if the parent club continues to pay the salary then often there is an upfront payment by the loaning team to offset this.
If the loaning team pays the wages then often there is little to no upfront payment, and teams negotiate whether paying 25% - 100% of the wages.
Soccer also has obligation to purchase options in loan contracts, I guess that would be obligation to trade a pick if this was in the NFL?
It varies. It would be a cool twerk, especially when your stocked with lots of starting caliber players who can't play in a single position, but would need a lot of rules. Don't know how you would legislate for teams that may want a player back if they had an injury crisis or whether to ourright ban that, and also whether loaned players could play against their parent club.