Some ideas I had

How to fix Stamina
No power from the power pools should be mandatory as they're just options to choose from. On the majority of toons Stamina is required. I think the base recov rate of players should be increased somewhat and the recov increase from the stamina be decreased somewhat, but stamina should be given a secondary end drain resist buff. This does a couple things. It turns Stamina from a "must have" to a "it'd be nice to have" power. Also the end drain resistance makes the power actually seem like a power as opposed to just giving you more endurance. Currently how endurance works as well as the next suggestion have always been a thorn in the side when making toons.

If everyone should have a travel power, why make it use a skill slot?
Quite simply put, travel powers is something all toons should have. So it should be a free power. I suggest making a small arc like the cape and aura missions that unlock a free travel power of your choice. It can be any one of the 4. When respecing you can change your choice. Also to balance things out so that getting multiple travel power isn't as easy now, in the travel power pools the travel power should be shifted to the 4th (final) slot so that you need 3 points in it to get it. The 4th power should become the 3rd power. You might say "what about group teleport and fly it wouldn't make sense to get group fly before fly." Well nobody really ever uses those powers. In fact a lot of people get mad when you use them. Just replace them with a different power.

Selling things should be easy
If I remember (been awhile since I played) when you put up an item you're charged 5% and when you sell it you're charged 5%. All the fee should come after you've sold the item. It should cost 0 money to put it up. Having an initial fee discourages players from taking down their item to put it back up at a lower price. Having the initial fee encourages a "let's wait a bit longer and see" approach. As said earlier.. selling things should be easy.

Now that the markets are merged, quality of life can ensue.
I think this suggestion might get some hate because admittedly this does not make sense conceptually. However I think the quality of life benefit from it outweighs that. Anyways my suggestions is to make money you earn go to your ACCOUNT instead of your CHARACTER. What I mean is that all your money on your account would pool together and all your characters would have access to all your money. If this ever happened (which I doubt but hey who knows) they'd have to get rid of the money cap though (the money cap is lame anyways since people can just siphon money to different toons). The reason this is beneficial is so you never have to log off and get on another toon then mail yourself money then log off then get back on your toon. Imo anything that forces you to switch toons then switch back is a bad thing. If you want to play the particular character you're on you should never have to log off it.

Only thing I could get behind is the last suggestion. Stamina is not mandatory. It just makes life easier. If you want life easier without stamina then slot for it. No need to change how the powers work. If you want recovery resists then roll a Dark Armor or Elec.

Travel powers are not mandatory either. Plenty of people now get around with ninja run just fine.

Pretty much what you are asking for is the ability to have 2 or more slots open up for other power picks instead of things that you feel are mandatory. Sorry, but the game is already balanced around the number of powers you have available. If you have a tight build and can't pick every power you want, then welcome to COX. WAI.

If there were no fees to list items, there would be no incentive to list items at a price that would sell. If you have to risk a bunch of money to list something at a high price you will be less likley to put in a price that will take forever to sell. With no risk you could put something up for say 100 mil if the going rate is 5 mil and hope that someone comes along that has a ton of money and the I MUST HAZ NAO attitude. If no one does you can relist at 80 mil after a few days. Still no bids? Try 50 mil. With that loss of Inf risk in place, the same person would never bother listing at 100 mil in the first place and instead would put it at a more reasonable price.

Cottage rule seems to apply here.

At this point in the evolution of the game if you changed Stamina at all be prepared for an unholy war on the forums. Stamina is not required. Only my Blasters find it really hard to skip, most of my others don't need it.

Concerning travel power changes. Not on your life. This would break so many toons as to not even be funny. While most of mine stick with just one, a select few use two. SS and Fly mainly. Concept reasons.
Why make it harder than it already is? I'd say just remove the restriction entirely but then you'd need to create a new City Traveler Vet reward as well.

While the initial fee has annoyed me when my level 8 gets an expensive drop and I can't afford to list it, it's there for a reason.