Did Life on this planet start out with one living cell or not?

If you truly want to know how life started out on this planet go get a Bible and read Genesis Chapters 1&2 it tells you how God made Man and women the animals the stars the sun and the moon all in six days and rested on the seventh day. Thanks for the question.

It is likely to have been microbal.

We don't know.

I find the theory of panspermia to be very persuasive

and IF that were an accurate theory

then life on this planet might have started out with one or more than one living cell.

Abiogenesis started life on our planet.

You know I have always been a firm believer in the old saying that there is no such thing as a stupid question. I stand corrected.

Nope

if that were the case what would it eat?

I'm not saying that life started when lightning struck a pool of primordial soup. But if it was *something* like that, more than one cell might have started because the chemicals and energy were all there.

However, it's assumed that only one of them had all the right stuff to survive and maybe eat the other ones.

No. Life did not start as a cell, cells came later once life appeared and evolution started. Life began as a replicator, a crystalline structure that could copy itself. Once a replicator appeared, evolution, change over time, kicked in and the replicator began to change. Even today there are crystalline replicators such as prions - the organism that causes mad cow disease - and viruses. These are much smaller and simpler  than cells.

I doubt it, but science giving itself a single-cell starting point

and then building on it from there, isn't an empty effort.

For now though, the answer has to be that we simply do not know.

Yes, however that single original cell was in existence long BEFORE Earth began. It then further developed according to the laws of physics pertaining to this particular planet.