Can I still go mess around before suicide mission? *Spoilers*

I just got done with the joker bit, which was rad. I was presented with a choice wheter to go to the omega 4 relay now or wait. I chose now and shepards response did not really affect that. I went to hte galaxy map and notice I can jump to other parts of the galaxy still.
 
Can I still mess around and once I am 'done' go to the omega 4 relay and come back with everyone alive(including crew)
 
EDIT: Sorry, please move to ME2 :(

Just finished on PC (survived) and got option to "freeplay / mess around and explore" after the game was over.

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If you dont go straight away, you lose the crew and Kelly, with only Chakwas remaining alive.

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Hmm, maybe i'l go to an earlier save.
 
I asked Legion about what he wants for upgrades, but I saw nothing for ship uprgrades that was different

"Hmm, maybe i'l go to an earlier save.  I asked Legion about what he wants for upgrades, but I saw nothing for ship uprgrades that was different "

You can get his sniper rifle. 
 
And I've heard you can do ONE mission (Legion's Loyalty) before people start dying.

Oh that it? Then I'm fine.
 
Guess I'll go in tonight!

This is one part I really didn't enjoy about the game.
 

I realixed I did not get legion is sniper rifle. So I went to a save earlier before the reaper iff.
 
Also, do i have to get all armor, weapon, prototypes? When i go to a store and I see that they are selling those stuff, is is the ability to research it or did simply buying it upgrade my rifle for example

Alright, I made it back with every squad mate alive and I saved the crew, including Kelly... I didn't even realize she could die till I discussed it with a friend. That would have torn me up completely.  Though I didn't go through the relay immediately, I must have bugged the game or something because I got to do the Legion Mission before the Collectors attacked, think I went down and chatted him up quickly before doing anything else and was immediately sent off to the mission.. I was finding it somewhat odd what happened, think I'm starting to see what they were getting at with it, cause when I went to the galaxy map after that, I was going to the shuttle for no apparent reason and then just suddenly returned after the attack.  Doesn't matter though, you're suppose to be able to do the loyalty mission first according to what I've heard.
 
Either way, I didn't do any missions... But I explored two or three galaxies to collect materials for the last upgrades, including Legion's rifle. I upgraded basically everything I could in terms of requested upgrade from the squad and also group buffing things like shields and armors, also as much as possible in terms of weapons. So that 'you're too late'-thing only applies if you do missions, not when scanning planets for resources. (don't take on the missions if you find any, of course)