I can give you some inside on market - if I have 21 players in my team I can bid for 2 more and I can buy both, but then one is not in my squad until I free up one slot.
Same thing with money. If I have 2 million left I can place 2 or more bids as long as they are under 2 mill. If I decide I want all players I bid on - I will get negative balance in my account, but the bids can be won even if you don't have enough money - I seen players bidding with negative 3-4 million even more. What hapends to your bank when you get negative balance is frozen until you bring the balance back to positive. You can not spend more money for players or stadium constructions.
I hope this gives you some answers to your questions. I've seen that most of the answer you got were not detailed.
Have fun