Kelenken yes I've already said Kaelesh has no good buildings unlike rock'tal. However, as I said, it's irrelevant because most of the early game life forms benefits come from the technologies and not the buildings. Anyway, I am speaking purely from a mix-max try hard perspective from new speed unis (not 1x), obviously if rock'tal is fun then choose rock'tal.
Rock'Tal buildings on the other hand are incredibly good and cheap enough to be used right from the start (1-2M points), so even if you are starting a new uni it is the best choice.
No, investing in resource production boosting life forms techs/buildings (or even mines) that early, especially before astrophysics 9, is not an optimal strategy. Everything should be going into LCs or astro 9 at this stage (even more so if your uni has a top rank guy abusing DM). As I said, the majority of early game income comes from expeditions and not mining. To focus on mining at this stage when it represents such a small portion of your income is very inefficient. To put it in perspective, at that 1-2M stage, my resource findings were 90%+ of my total daily income. In fact, even though my economy is top 10 on my server, my expedition results completely dwarf my mining. On my small active discoverer account a single 1hr expedition could return more than my daily income (indeed, this happened today)
So basically you would be choosing Kaelesh only to get expo tech without random picking, but getting it at random is not that hard since it is in the first tier. All you need is a little effort and patience and you'll get a good tier after several retries.
Yes this is entirely the point and yes it is very difficult to random techs and increasingly more so the more techs you want. Both expo res techs and even the expo ship techs are vastly superior to all other life forms techs and buildings for an early game discoverer account. So much so that all other techs combined have a negligible effect on income - nothing more than glorified really good plasma techs. Given that there is almost no downside to switching, it makes perfect sense to treat kaelesh the same way people treat discoverers - use it to grow fast up to the early late game then switch later