Hi guys, any constructive criticism about this @500 pts team?

Here goes the team:

I might not be up on rules but IIRC you can only use one ATA.

Also: you can only use ATA if you fielding theme team.
Killraven and Bucky break the Avengers Theme and Killraven and Alexis break the Soldier theme.

You're right about that. They all need to have a common keyword to be considered a theme team, and then you could choose one ATA (and only one) that any of their keywords qualifies for. It doesn't have to be the common keyword, but each figure that has the ATA keyword has to pay the point cost for the ATA.

In short, I'm not terribly optimistic about this team. It's serviceable, but it's heavily affected by power creep. Your threats' defenses are pretty low, so you're fairly likely to get hit. Yeah, the Secret Avengers ATA helps keep your reducers on you, but that can still be run on newer pieces.

FI201 Captain America: I'm assuming this is the figure you most want to play. I would see this as a hybrid secondary attacker & support. He's a little weird in that his top click tries to get into combat, and that trait is daring your opponent to take him out. I'd want to push him to click 2, but certainly won't neglect the 5 damage he can offer to start the game.
ADW011 Captain America: I'm pretty sure you picked this for the first one's trait. While I feel dying should rarely be a strategy, you did at least choose a very good Captain America. This one is all support to me with that amazing Leadership, though he's got the stats he can bring a little offense. I wouldn't necessarily put the first Cap's legacy on him, though. +1 speed & attack is always welcome, and it can be given to someone more capable of combat to be incredibly effective.
AOU009 Alexis: Clearly your Probability Control piece, but it can also be used to transport your team. I feel like there's probably better PC pieces out there, but this one's maneuverability is certainly nice.
GOTG019A Captain Marvel:That damage power on the top click is really solid. However, I don't think it justifies the rest of it. This Captain Marvel just doesn't hold up. Granted, I've only been in the game a couple years, but looking around Captain Marvel, I don't see many good pieces. I'd say that has changed recently, though...
* No comment on Killraven & Bucky, as you need a theme team for the ATA, and their roles aren't terribly hard to replace.

Suggestions for replacement
Secret Wars did make some workable Captain Marvel pieces, even though I wish they were more range focused. The prime is probably better, but the basic rare is solid, too. For availability's sake, I'll assume the basic rare is used. This leaves 152 points to build.
Killraven's got a very interesting ability, and I can totally see him getting played on a GotG team to great effect. Fortunately, the Avengers have access to a similar piece. I have always loved this Beast on my X-Men teams, but he has plenty of named keywords to play the field. He doesn't even need line of sight. They just have to be within 4 squares. Killraven's definitely good, but this Beast will do the job slightly better. 47 points left (42 of which can be a character due to the ATA).

Bucky looks like he's kind of filling points on that team. Copying team abilities is nice, but neither of our teams has much in the way of abilities to copy, and whoever we include for this Avengers team will already have the ATA. At 42 points, there's an absurd amount of things you can do. You already have Probability Control & Outwit pretty well covered here. Unfortunately, I don't see much in the way of good Perplex at this cost for Avengers, but I think a good healer would help nicely.Depending on your opponent's team, you may be comfortable sending her out into the field, but don't get too confident about her trait protecting her. Someone this good at healing will probably help your pieces stay relevant throughout the game. Should the opponent actually kill someone next to her, you get some level of a 100-point threat in return.I'd say as long as you don't roll a 4, you'll get good use out of her.

This makes 12 points left over for whatever filler you want to include. I've always loved the Bloodaxe on Beast, but an Asgardian Shield could always be helpful. ID cards can also be good if you have any.

Force Build 9082460 0
Set	#	Name	Team	Pts	Value
FI	201	Captain America		88	$2.70
ATA	064	Secret Avengers		5	SELL
ADW	011	Captain America		50	SELL
ATA	064	Secret Avengers		5	SELL
AOU	009	Alexis		65	$2.45
ATA	064	Secret Avengers		5	SELL
SWB	037A	Captain Marvel		125	SELL
ATA	064	Secret Avengers		5	SELL
UXM	050	Beast		100	SELL
ATA	064	Secret Avengers		5	SELL
TMT	022	Jane Foster		30	SELL
ATA	064	Secret Avengers		5	SELL
Force Total:				488	$5.15

Hello and thank you everyone for this amazing feedback. I've been busy lately and I'm going to read and respond all of these messages shortly.