If millions of chance mutations are needed before one truly beneficial mutation can emerge, then what becomes of those mutations that are not immediately fatal to the organism and are passed on to the next generation?
They get passed on to the next generation, with no discernable problems. Most human genes have dozens or hundreds of alleles. Any number greater than four would have to have arrived after Adam and Eve, via mutation. So yes, lots and lots of mutations that are very weakly beneficial, or very weakly harmful, to the point that they neither increase in the population nor are removed from the populations
Such deleterious mutations would, from a statistical standpoint, far exceed the number of supposedly beneficial ones.
The ones that don't actually harm or help an organism are called "neutral mutations." Most of us have several dozen that neither of our parents have. Few of them really do anything as far as selection is concerned. Because they are so close to the useful/harmful boundary, they might be useful in one particular circumstance, and harmful in others. These, as you see, tend to persist because there's no benefit or harm to them. On the other hand, a few mutations are harmful. These tend to be removed from the population by natural selection. A very few are useful, an they tend to increase in the population, because they make it more likely that organisms having them will live long enough to reproduce.
Thus their inevitable entry into the gene pool would result in the progressive deterioration of a species and its eventual demise.
That would happen fairly quickly, if it were not for natural selection. Occasionally, these improvements will lead to a relatively isolated population becoming reproductively separated from the rest of the species. This is how macroevolution occurs.
4. Life cannot develop except in the form of a living cell, the smallest possible self-sustaining, self-reproducing organic unit.
Here, you've confused evolution with the origin of life. Two different things. Darwin merely assumed that God created the first living things. Evolutionary theory merely describes how living populations change.
The really impressive thing is that as we learn more and more about the complexity of the cell, the more we see evidence for the evolution of this complexity. Would you like to see some examples?
In addition, the mitochondria are known to possess their own DNA and RNA, which is completely different from the DNA and RNA found elsewhere in the cell.
Technically, they are separate organisms that are endosymbionts living in eukaryotic cells. They resemble bacteria, and are descendants of bacteria that formed an endosymbiotic relationship with eukaryotic cells. They even have circular DNA like other bacteria, and their cell membranes are bacterial membranes.
Is there any evidence that such endosymbiosis can evolve? Turns out, there is:
Bacterial endosymbiosis in amoebae
Trends in Cell Biology
Volume 5, Issue 3, March 1995, Pages 137-140
The large, free-living amoebae are inherently phagocytic. They capture, ingest and digest microbes within their phagolysosomes, including those that survive in other cells. One exception is an unidentified strain of Gram-negative, rod-shaped bacteria that spontaneously infected the D strain of Amoeba proteus and came to survive inside them. These bacteria established a stable symbiotic relationship with amoebae that has resulted in phenotypic modulation of the host and mutual dependence for survival.https://www.sciencedirect.com/science/article/pii/S0962892400889667
And since they are self-replicating, they are produced only by an earlier generation of mitochondria – the cell nucleus itself cannot produce them. Thus, in order to function properly, a cell must contain an energy-producing organelle which cannot survive outside the cell and which the cell itself cannot produce!
Nope. For example bacteria and other prokaryotes do fine without them. And many eukaryotes don't have them. They didn't tell you that, um?
To believe that something this complex could have arisen by chance
Would be to ignore Darwin's discovery of natural selection. And as you see, the evidence shows the evolution of mitochondria from free-living bacteria forming a symbiosis with eukaryotes. We even have one directly observed case of this happening.
Before cutting and pasting this stuff, it's a good idea to go check it out for yourself; creationist websites often lie to you. Or, in many cases, they don't know any more about it than you do.