Hi Anna,
Sorry I JUST got on today, was in Maryland at my parent's home.
NO,NO,NO! Don't wait until you've "lost more weight" to add these workouts! Add them now!
The greatest words to EVER come out of Cathe's mouth were, "don't be afraid of heavy weight, they do good things for you!" They certainly do! PS Series and S&H Series will allow you to focus on slower training, and adding heavier weight (at least heavier than you'll probably do with PH). The best way to get the most out of both series is to REALLY push yourself to do the heaviest weight you can for each exercise. Write down the weights for each exercise that you started with, and every 2-3 weeks, see if you can push yourself up a notch. Some muscle groups are easier to progress with than others. For me, shoulders and biceps were/are my slowest to increase weight with, but challenging the muscles is what you're shooting for.
So whenever you're ready to add either series, go for it! You won't be sorry!
Donna
p.s. word of warning about S&H. It made me REALLY hungry the first time I did it. I couldn't manage to stay within my target calories on the days I did a S&H workout, and I noticed the biggest increase in protein intake during those weeks. Many others have commented on being more tired during a S&H rotation, I didn't have the tiredness, but the hunger thing was scary at first when I didn't expect it. So you may want to plan a "power snack" or 2 in your day just in case. I'm always prepared now when I do S&H.
Fitness~ it's a journey, not a race!