Newbie from Brittany, soon building Gale IV 1/8 scale

Hi thanks for accepting me in the forum. I moved around quite a bit during my working life, including 6 great years in Portland OR. I am now happily retired in Brittany, by the sea, fly fishing, sailing, and building model boats during the winter. I mostly build from scratch, essentially wood, but also fiberglass or carbon fiber. A couple of years back I build a 1/5 scale small outboard powered hydro, based on a 50's Hal Kelly design named Jupiter. I got hooked and wanted bigger so now I just ordered a kit from ML and a plan from Newton Marine to build an 1/8 Gale IV. I am confident I can build a decent boat, but much less so regarding the motor/esc/batteries setup. Since there is no racing around here and I'll probably have to mix in with slower boats, I want a fun boat that goes reasonably fast, not necessarily one that goes over 90 mph. I looked at the class rules, the 3 approved motors, all running on 8s, seems a lot of power to me. Could I go for such a motor and tame it by going for 6s, until I go crazy and rig an 8s setup, or should I choose a different motor? Second question is there any schematic on how to rig 2s lipo batteries to get 6 or 8 s somewhere? Sorry for a lengthy post and thanks for your help
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If I get this wrong someone will correct me I'm sure. You want to wire the batteries in series example two 3s batteries in series = 6s . If you do a search on the forum there are diagrams to go by . The connector with the connector with red and black wires and the larger gap in it goes to the esc . My proboat Zelos twin 36 uses 2 of these cables.