I started playing Heroclix when I walked into a comic shop in late 2002 and saw a painted miniature of Aquaman in a display case. When I realized, 'I can play the Justice League as part of a GAME?!' that was the start of a journey of about 500 tournaments filled with thrills, anguish, and a startling amount of misses by one (I'm pretty sure I hold the pan-galactic record. In one tournament I missed by one 13 times. 13.).

When I saw the Justice League as a Team Base (albeit minus Martian Manhunter) I was over the moon. Then I saw its powers and winced. I played it the day it came out and then again a few months later for purely "defensive" purposes, thinking there would be some serious cheese at a certain tournament (I know, I know, that's never a good reason to play a fig!). Now I'm thrilled that I can play the JLTB in broad daylight and not be pelted with rocks and garbage.

With that in mind, I want to make sure I understand the changes.

Assuming it's fielded with all seven Team Members, please let me know if this is correct:

The 300-point version gets +3 to initiative and two free actions
The 400-point version gets +4 to initiative and two free actions
The 600-point version gets +6 to initiative and three free actions

Is that right?

You got it spot on.

Glad I got it right! When I play the 600-point version, should I do the Solo Adventure thing as much as possible to make up for the lack of actions?

Does the team base still have access to the ranged combat action and close combat action, move action as well as the power action
on top of the the free actions?

I think you can only use the free actions to do any of those actions. So with the 600-point version, if you take one ranged combat action, one close combat action, and one power action, that's all you can do.

The same amount of actions they had before are still there; and yes, I'd believe that this encourages Solo Adventuring more. Team Bases have simply become more fun.

does the -1 damage stack? up to the rule of 3?

Does Outsiders T.A. counter that modification?

Yes to both @bam

Actually a better way to respond is "please explain why you think it would not"

Is it a modifier? Yes
Does Outsiders prevent modifiers? Yes
Are modifiers subject to the Rule of 3? Yes

Soph, I would only think not because I doubt Wizkids intended that. Now, whether or not they actually do anything to prevent you from using Outsiders to remove the minuses is another story.

I thought the same thing at first but after reflecting, I doubt it will be changed. If you have to burn your outsiders on your team base you won't have it to weaken the opponent so a balance should be maintained.

I played the 600-point version in a pickup game today. We played on the Chaos War Avengers Mansion map so there was a strip of hindering terrain between my Force and his. It was like Pickett's Charge. Every time he would try to bring his figures across the map I would use Solo Adventure to put out a new fig (I managed to get four out) then take the other two actions to mow down his figs before they could get close. It was a slaughter!

I'm not sure how the 300 or 400-point versions will fare so I'll give them a try soon.

We've heard of the Outsiders TA and are aware of how it affects modifiers

It's a valid tactic. It locks you out of any damage bonuses though, like RCE or Perplexes.
That does lock the TB's defense value as well, meaning it can't benefit from Hindering, ES/D, Combat Reflexes. it's definitely a risky enough move with enough drawbacks that I really can't see a reason to disallow Outsiders TA to target Team Bases.