I think i'm going to go ahead and buy both active and passive SP Boosters pretty soon. Now my only question is: When should I activate these for the maximum benefit? Or how would you recommend using them?

Passive boosters can be activated whenever, preferably the instant you acquire them because why not? There's no downside to a passive booster, they don't interfere with anything or prevent you from using an active booster at the same time

As for active boosters, they boost any sp you gain in battle by 1.5x. If you're not already aware, the boosted SP granted by the active booster does not count against the ~190k "bonus" SP that you get while playing over the week that resets every Wednesday, it just adds onto it. You should use the booster before you start using up that weekly bonus sp to get the most out of it!

If you activate a 7 day booster on a weekend, it is reasonably possible to hit your bonus sp cap before Wednesday, and hit the cap again when it resets on Wednesday but before your booster runs out next weekend, giving you two weeks worth of boosted sp for the price of one booster.

If you really no-life it, you can achieve the same thing using a 3 day booster on a Tuesday

Hell, if you're a ******* cyborg that doesn't need to eat or sleep, you could do it with a 1 day booster by starting ~9 hours before downtime on Wednesday and really save yourself some aur

After the bonus sp runs out the active booster will still boost the soft cap SP, letting you get a max of 1,500 sp per battle instead of 1,000 (assuming you can pull 1,000 warpoints out of the battle). That extra 500sp still adds up if you play a lot.