jjf3 - way you phrase problem is inaccurate. It sounds like there were freely floating single-celled organisms and just out of blue they decided to mate. It's not like that
It all started with colonies of same single-celled organisms, that benefited from sticking together. Thanks to evolution - random mutations, and natural selection those who evolved to deepen this "cooperation aspect" (by making long strings of cells, bigger, heavier lumps of cells, or something) survived because it worked well. So first step is many identical cells. No problem with your problem numer 1. Also no problem with number 2, since first they just spawn single-celled organism that had tendency to aggegate.
Problem number 3 is abiogenesis. It's entirely diffrent thing than evolution and passage from single- to multicellular organisms. Abiogenesis is still unsolved issue (but we have some ideas). Exploration of Titan may give us some answers, since it's kinda like young Earth.
Panspermia has it's charm, but it's not likely to be the case. Due to timing of emergence of life it's much more likely that life emerged on surface of Earth, and didn't come from outer space.
Problem number 4 is... well "G" word is just an easy answer. Scientific community doesn't say it just happen, it's evolution. Thanks to some errors some bacteria started conjugation, and it worked. Bacteria that performed conjugation survived and spreaded this mechanism.
Problem number 5 - as I said, it seems unlikely (but it's possible for life to travel like that, and survive trip and entering atmosphere)
Problem number 6 - Evolution baby, evolution.
Problem number 7 - By holes you mean that there are no fossils. It takes lot of luck - organism must die in very convinient conditions to be fossilised, and we have to be lucky enough to dig it out. Serious problems may be present when there's no idea of what would intermidiate organism look like, how it could change from say... thin to paw, but there are pretty much no holes like that anymore (say hello to Ichthyostega). Once enemies of evolution pointed eye as something that couldn't evolve "just like that". But we found organisms with light sensitive cells, and discovered whole process how in tiny steps very complex eye emerged. Actually it turns out eye evolved many times independently, and that makes it very strong indication, than extraterrestial life, that has access to visible light will too use that. So don't you worry, evolution tree is pretty much figured out, and we're filling holes as we speak.
General thing is - evolution is being proven over and over, while "scientific creationism" is just called "scientific" for no reason, since it's just talking out of ass. No scepticism, no review of errors, no self-checking.
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