I don't think the reason why they kept up the masquerade so long was because of any tactical advantage or anything like that. Warriors or not, these were still just kids. They didn't want to give up their lives to fight this war full-time, and so they didn't do so until it became clear that there was no other choice.
I agree that it would have been a better idea to go underground sooner. I think they were taking a big risk, leaving their families (not to mention themselves) out in the open. And they could have hurt the Yeerks a lot more if they had inducted their families earlier, giving their families a better chance of getting used to the new reality so that they could be much more helpful than they actually were in the final arc. Heck, maybe they could have even given their parents morphing powers, and allowed them into the team.
Not to mention that, if they'd acted sooner, Jake's family would have been saved, FTW.
All of that said, in the Animorphs' place, I still would have done exactly the same thing they did. Just laid low, and tried to keep a quasi-normal life. Not a good tactical move, but the Animorphs were so much more than just tactics.
As for the guerrilla cell groups idea, I've heard that talked about before as something the Animorphs should have done. The idea has merit, but you have to consider the security risk. Even if you gave the other cells absolutely no information on the other groups, if any of them were infested, it would still be revealed that they were human. And if the Yeerks ever realized that any of whom they were fighting was human, then they could have pulled what they did in book #49 earlier (ie, testing blood samples for matches to find the Animorphs). And if they had ever actually known in book #49 that a number of the forces opposing them were actually human, rather than just speculating that that was the case, the Yeerks would have tried harder to keep that operation secret, and maybe, just maybe, they would have found the Animorphs before the Animorphs even knew they were looking. Bam. War's over.
And its a fact; the more Animorphs you add, the more likely it is that one of them will eventually be made into a controller. So you can't just keep adding more and more 'cells' and increasing your forces. Somebody is going to get caught eventually.
Truth is, the small group they had worked well. It minimized the security risk, while still allowing them to inflict damage on the Yeerks. Keep in mind, of course, that up until, what was it, book #46, they were just holding the Yeerks at bay until the Andalites came to the rescue. They weren't trying to defeat them all by themselves.
