Apologies for the late reply, and thanks for your interest ^v^
Most restraints will give a buff to strength, but they'll also have some hindrance like draining energy and raising arousal. Some may drain strength until it becomes a debuff. They may also build up hypnosis or other status effects (some kinds of curse/corruption and goo coating are planned) over time. I'm still thinking about what to do with arm and leg restraints, but I might have the heavy ones weaken basic attacks and make movement slower during combat.
The arms and legs are actually combined on the little body diagram, so I had 8 parts and 8 corresponding restraint slots planned. However, I recently decided to remove the body diagram and replace it with a big "paper doll" sprite with layered parts, similar to some other lewd games. I'm also splitting the chest and groin areas into inner and outer layers, so it will actually be 10 total restraint slots! As for the number of restraints, I'm going to have a bunch, maybe 5-10 per themed location, some of which will have variants for multiple slots. I'm also coming up with combo restraints, and the demo will have a few that you can only get by combining the more basic ones. I'd especially love to keep adding more of those as development comes along.
Back to the body diagram and why I'm scrapping it; the idea was that Piko's body parts could be targeted and drained of their power by attacks/restraints. This would reduce her strength and innate energy regen until restored. I think this system had potential, but it felt redundant when I already have strength-draining restraints and could do regen in a more player-controlled way. I found it more interesting as a clothing stat that could be considered in the player's build.
There will be quite a few parasitic and symbiotic restraints, yes, and there's already a little blobby one going into the demo. Some just latch on and do their thing. Droning, gooification, corruption, hypnosis, I could make one for every status effect and probably will eventually. Others may act as breasts, a penis, or an udder that fills up with Piko's energy. While they may help certain enemies drain her more easily, they could also fuel some of her attacks (when I design a "milk build" at some point).
Whew, thanks for bearing with my long-winded explanation. The past month's been busy, but I'll be updating the game page when I make my next post showcasing the player doll.