3 is the only one I could answer with any certainty, with justification.
And the answer is 'no'. Insects don't have circulatory systems, they get oxygen to, and waste gasses from, their cells by just having holes in them (effectively). This is highly inefficient for anything but the smallest creatures, hence the need for blood vessels and the like in larger critters. Furthermore, if you just scaled them up, their structure wouldn't be able to take the weight (look at a relative comparison between a fly's leg and an elephant's leg, compared to their bodies, for instance), and they'd collapse, although that's not about insects per se, that's about scaling ANYTHING up.