2. More importantly, would i be able to form a healthy population, several generations, from a single flowering plants - or is the fact that all of the resulting generations comming from a single plant would be weaker in some ways then if i were to have a group of plants fertilizing eachother and introducing diversity to the gene pool?

As far as the pollinating question, you are asking something a little bit to broad to be answered in a simple forum. I'll address one issue: many of the flowering plants that we purchase today are hybrid crosses. They will not reproduce true from seed. Others are grafts or otherwise cloned and will not reproduce true from seed.

You might want to make a list of the specific plants you are interested in and do an individual search on reproduction of each.

Since pollination is only the physical act of a pollen being placed on the stigma. The possibility is high. Whther or not fertilization occurs would depend on the plant some plants have chemical mechanisms that prevent self fertilization. Or if you planted one of the few plants that only produce only flower of one sex on the same plant self fertilization would be impossible.

2. More importantly, would i be able to form a healthy population, several generations, from a single flowering plants - or is the fact that all of the resulting generations comming from a single plant would be weaker in some ways then if i were to have a group of plants fertilizing eachother and introducing diversity to the gene pool?

The health of the the resulting population would depend on the heterozygosity of the original plant. If the original plant was severly inbred you may see some weakening of the plant population. Since the offspring from the first plant would have some genetic diversity there would always be some variation in the plants. A group of plants may not be gentically diverse to begin with. If you started with a group of plant that were asexually propagated or a group of F1 hybrids created from inbred lines you would have the same results as if you started from a single plant.

Other things that would effect the results would be if you were using an annual or a perennial. If using perennials you would have the possibilty of offspring breedins with the parent. Also generation time would effect the results.

That depends on the particular species because some species are primarily self-pollinators and others are primarily cross-pollinators. There are some species that must be cross-pollinated. And then there are other species that may self-pollinate or cross-pollinate.

The species that must be cross-pollinated have what are called self-incompatibility genes that cause self-pollinations to fail.

More importantly, would i be able to form a healthy population, several generations, from a single flowering plants

For self-pollinating plant species the answer is yes - that is their normal method of producing seed and the offspring will be perfectly normal.

For plant species that must cross pollinate no offspring will be produced.

For plant species that permit both types of pollination the offspring will be inbred and that produces some individuals with problems. As long as the individuals that are unhealthy/abnormal/poor are removed from the group before they flower you will be selecting for vigour and that will help balance the original inbreeding and help produce a healthy population. There would need to be a balance between the number of plants left to grow and the number you remove. If you remove too many you increase the potential inbreeding level; if you remove too few you increase the loss of vigour in the population.

Taking cuttings of the original individual plant and growing a large number of identical (clones) plants will leave the possibility that all of them might die if the environment changes and they are not adapted to the change. A mixed (genetically) group of offspring (even from a self-pollinated plant) will have genetic variability and some chance of surviving such changes.