>Warlord
He got in a lot of wars because the pagans of the time fought the Muslims a lot.
Islam doesn't need war to spread. A lot of Muslims of the time were travellers or merchants, and they would share information about the religion as they went about their business.
>Marriage
You'll find loads of different ages on the matter. I've seen ages from 6 to 18. At the time the pagans of Arabia didn't use his marriage to Aisha (RA) as a way to attack him, which means it was seen as normal.
Aisha (RA) became one of the most important Islamic scholars of the time, and revealed loads of hadith on more intimate matters. If anything bad happened with her she would have mentioned it.
>Kaaba
It's a point of reference. If there wasn't a standard direction to face while praying, mosques would be annoying to walk though. You're not supposed to walk in front of someone who is praying, and if everyone is praying towards everywhere you'll have a hard time avoiding them.
There is a hadith where Umar (RA) is touching the black stone in the Kaaba, and mentions that he knows it's just a stone and can't provide any benefit but he's doing it because that's what he saw the Prophet (PBUH) do.
>Quranic errors
You'll find a lot of sites that twist the English translation to make it look like the Quran is wrong on things. I don't know enough Arabic to disprove them myself, but googling rebuttals for these "errors" should provide proper explanations. One they like to use is how the Quran states that the moon emits light, which the original Arabic doesn't say.
An important thing to remember when looking up arguments against Islam is that there are a lot of people with a vendetta against it. They will use as many arguments as they can, regardless of whether those arguments actually hold ground. All it takes is for one person to read "Muslims worship a pagan moon god" and not look into it, and you have someone ready to spread easily provable misinformation.
It doesn't help that people tend to stick to things that agree with their worldview. A stereotypical antitheist isn't going to look for rebuttals for the stuff he finds on sites like WikiIslam because he wants his worldview to be right. This applies to pretty much anything people can have strong views over, which is why looking at multiple sides of an argument is so important