There's a lot there, so I'll only address it in brief, and take more specific questions one at a time if you have any.
When you look at most of these stories as a whole (i.e. not picking out details to make a comparison look convincing) or more closely, most of these theories fall apart. Looking for similarities and parallels and making a big deal out of them is known as parallelomania, and is a frequent phenomenon among those eager to disprove something like Christianity. For instance, a certain title might have been used in that general time period to honour its holder. If the title was given to Jesus, but also possessed by someone before him, that's a weak similarity, especially when there are hundreds of titles given to Jesus, many, if not most of which are not original. By conveniently forgetting details, and giving unmerited importance to others, two stories can easily be made to look like they are significantly similar when they really aren't. I'll try to illustrate this with a simple example:
John J. Smith went to the store to get an apple one fine August morning. When he got there, he discovered that there were no apples available, so he decided to get a banana instead. When he got to the checkout counter, he realized he didn't have enough money to buy the banana--he had brought only enough for the apples, which happened to be cheaper. Finally, he chose to get an orange, and left with his purchase. Walking by a fruit stand on his way home, he saw that there were oranges for sale that were far cheaper than his orange, which he hadn't even wanted. He angrily went back to the grocery store to demand his money back, but was refused and stormed off, leaving his uneaten orange behind.
One hot summer afternoon, J. J. J. Schmidt felt like some ice cream, as he had been working outside all day. So he found an ice cream stand and asked to buy an ice cream sandwich. The ice cream man procured one for him and demanded $5.99 plus tax. Mr. Schmidt discovered that he had only $4.56. With a furrow on his brow, he looked to see if there were more affordable treats, and saw that dilly bars only costed $3.99 plus tax. So he bought one of those instead. After eating his dilly bar, he happened across another ice cream stand. This one had ice cream sandwiches for $4.50, including tax. Dismayed that he had wasted his money on a less desirable treat than an ice cream sandwich, he tried to bargain with the ice cream vendor, promising that he would pay for an ice cream sandwich the next day, plus 20% interest if he could only have one now. He even promised to make a down payment of 36 cents, but was refused. He threw his loose change at the startled vendor, saying that he could "keep the change," and stormed off.
Let's see how many similarities I can find:
1. They both have the initials J. J. S.
2. They both hoped to buy something specific but were unable to.
3. They both chose something else instead.
4. They both payed for it.
5. They both found another place with cheaper prices.
6. They both tried to bargain for something.
7. They both hoped to save money through their bargaining.
8. They were both refused what they wanted.
9. They both stormed off.
10. They both left something behind.
11. Both the stories happened during the summer.
Admittedly, in this case, the stories were based off of each other. However, the differences are significant. It is easy to imagine that they could have been written independently of each other. The list of similarities seems persuasive without reading the stories, but one can see that the stories, while they have their striking similarities, are not really that similar.
This is much like the Sumerian flood myths and creation stories, which are actually quite different, although the Biblical story is likely based off of it, or at least has a common origin with it. The Biblical story has a very different focus and is based on a very different theology than the Sumerian one.
With most comparisons of Jesus and another person, the similarities are even more far-fetched. Sometimes he is compared with people who lived after him, or his story is compared with stories that have a later origin, and we are expected to think that this shows the lack of originality in the Jesus story. For instance, it looks like that list of other "Jesus Christs" includes Mohammad! He lived in the seventh century, and his story is based on Jesus' if anything--not the reverse! Not to mention how vague the description is which determines what goes in the list. Laying the foundation for the salvation of the world and then ascending into heaven is quite vague. Lets take a look at Mohammad, for example. He supposedly received a new religion that "corrected" the Jewish and Christian religions. Supposedly he ascended to heaven for some of his visions. Note that he did not ascend into heaven, like Jesus did, at the end of his life, but only in his visions. Also note that he was only a mouthpiece of God, according to Islam and himself, whereas Jesus claimed to be God himself and spoke authoritatively, not just as a prophet, which is all Mohammad claimed to be.
I can't recall ever hearing the story of Horus resurrecting after three days and ascending to the heavens. According to Wikipedia, he triumphed over Set, and wasn't killed at any point in the story (unless I missed something--I did read it fairly quickly). It isn't unknown for things like that to be wholly fabricated, or for the story to have its origin after Jesus, with the Jesus story seeming to copy it because the characters in the later story are older.
All that is typical of parallelomania, as are long-winded lists of similarities that fall apart upon closer examination.
So those are my, um...brief thoughts about that.