Well, the augments have a cap based on the quality of the item. For example, weapon damage caps at 300% on a ramshackle and 700% of an ascendent. So you're almost certainly going to have to augment after you upgrade anyway.

is there a limit on how many different augments you can put on one item?

They're labled armor or weapons so you can only put them on whatever they're labled for, and you can stack all the weapon labled ones on a single weapon.