To address your questions:
1. Generally subcision (I assume with some collagen stimulators) will lead to collagen stimulation, and this is also what CO2 laser aims to do. Some experts suggest that an interval of at least 4 – 6 weeks is kept between each collagen-stimulating treatment for optimal results. There is no real good answer – as social downtime and other considerations have to be taken into account by the doctor in recommending the treatments.
My personal preference though is not to stretch the treatment too wide apart – 6 months does seem to me to be a little long. I would expect that would lead to reduced efficacy and perceived poorer results due to the natural progression of collagen breakdown over time.
2. Fractional lasers in general have a risk of hyperpigmentation. They also can result in acne outbreaks in some patients (especially those with active acne), and even re-activate herpes/cold sores. But these are generally manageable adverse events. Social downtime is probably the main problem patients face.
As such, do get your treatments done early to have optimal results, and your doctor should be able to advise you further on the treatments.
Wish you well!
