The best cooling strategy is to overspec the discharge of your battery so far that you can wail on it all day and never notice a heat difference between ambient temp and battery temp, even in the low 5-10% range of the SOC where internal resistance exponentially climbs as you approach 0% SOC.
I started my ebike hobby out with 36v 20AH 20C lipos and a 250W motor. The voltage sag was about 0.1V on an 15A load. Then i moved to a 1500W build and saw ~0.5V on a 40A load. Still no perceptible heat. Only until i got into a build that did ~2500W continuous, 4000W peak, did i start seeing that pack get slightly warm and dropping a few volts under the full 80A load, although the battery was 6 years old by then, which is totally acceptable to me.
I generally recommend people take the maximum continuous C rating of any cell and cut it by 1/4th the rating. This will give you VERY long battery life, excellent discharge efficiency, no heat issues, maximum performance, maximum watt hours, and maximum range out of any cell. And as the pack ages and the internal resistance climbs, it still remains tough until the day it dies.
And in fact, if you ride in freezing conditions, nearly every lithium cell's internal resistance quadruples, so in freezing temps, only then will your pack start to operate like a commercial ebike pack.. IE only delivers 90% of promised range, 4+ volts of sag, etc.
OK, as far as rigidity goes.. the more your pack is 'one' with the frame, the better. Bolt/strap down/jam that into an enclosure as snug as you can get. This is super important for an 18650 pack with dozens if not >100 little interconnects that could, over time, separate due to constant vibration. The more the pack can move on a frame, the more you multiply the vibration as you smack potholes 'n crap on the road.
I've always used lipo packs so this is not a concern. My series-parallel interconnects are 10 gauge wires and there is zero movement between the pouch cell and the little circuit board that the pouches are welded to. I would point the lipo packs upwards so that the interconnects never touched anything. In addition, i'd duct tape the packs together as tight as i could so that they were all one large assembly. Then throw tons of padding underneath so that as i hit potholes, the bottom of the cells have some kind of suspension.
I do not have as good of a solution for 18650's. You've got interconnects at the top and bottom of the cell. You've got tons of cells in parallel/series. I'd imagine that the best way to build an 18650 pack would be with spacers so that the spacers take the impact before the cells and interconnects get hit with the vibration. The larger/heavier the 18650 pack, the more this is a concern. But what do i know? i've never built an 18650 pack so i'm just playing the engineer version of fantasy baseball here.
