With the understanding that the series would have been dramatically different in such a scenario, (and with all due respect to HA3) the Anis COULD have easily had an over-arching strategy... They just didn't because they assumed that the only requirement on them was to "foil whatever the yeerks are doing", and because they felt that that requirement was already a lot to handle...
In fact, after David, the Animorphs would have done well to rebound with more "experiments"... Instead of just picking whoever happened to be lying on the pavement in front of them at the moment, (i.e. David) they could have carefully controlled who they chose, and the surrounding circumstances...
They would have had to choose members (ideally from their own age group), that they knew they could trust... people they could watch for three days and be sure of their freedom... people who weren't on power trips, or were prone to psychosis...
Also, it would have been better to add them in small groups of three to five, so as to limit the "new guy" feeling... this would also immediately give the new members a feeling of belonging, as they would be grouped together as a team... kind of like an antithesis to the Sharing...
They could then continue this pattern, spreading out and using cell tactics... The sudden onset of multiple "Andalite Bandit" attacks would not be a problem... the yeerks could be free to assume that the Andalites had begun to recruit humans to their ranks... That doesn't change the fact that they don't have a clue who they could be...
With such a network, and yes, "army", at their disposal, the Animorphs could have gone on the offensive, especially if they stockpiled weapons and technology while they were growing their ranks... The yeerks would have been forced to either go public with the invasion (an unwise option with so many dangerous covert soldiers now saturating Earth's forces, or pull back and try again even more subtly (an option that V3 would never condone - but it's very likely that the addition of hundreds of "Animorph Bandits" would be a failure that would certainly merit the removal of the Visser...