Satan

A lot of things are said about what is and is not possible regarding dreams about Ahl al-Bayt (A), however, as far as I know, most of them have no basis.

It is possible for the Shaytan to appear as something he is not; in fact, the main feature of Shaytan is deception. 

However, even if you were dreaming about something other than Ahl al-Bayt, there are a lot of things between Ahl al-Bayt and Shaytan that you could have been dreaming about. (Including your own subconscious!)

If, in your dream, the being told you to do something evil or which you know is wrong, it is good to ignore it. It doesn't really  matter where it came from. It could have been Shaytan or something else. 

If it told you to do something good, it is good to accept it.  

If it told you something else, you can also look into it and see if it is a beneficial or destructive thing. 

If it just stood there and didn't do anything, then it doesn't really matter - all you can say is, you don't know. 

So, I don't think you should worry too much about Shaytan being in your dreams. While it is good to be conscious of Shaytan's existence, it is not good to get too paranoid about it (indeed, that could also be a trick of Shaytan!). I think Shaytan is probably busy in other places and maybe doesn't have too much time for dreams unless there is some very specific reason why you think this is the case. 

(This is assuming you actually had a dream about this and are not just asking in general)

It is said that the garden that Adam and Eve were in was a different garden than the one that people to go eternally in the afterlife.

Allameh Tabataba'i brings up this question in Tafsir al-Mizan (available online) in the section on narrations 2:35-39 and discusses it in light of the narrations. For more elaboration on this question, as well as relevant narrations, where the garden might have been, and so forth, you can read that section.

I have not come across the idea that the angel Mika'il keeps the devil out of heaven in mainstream Shi'i or Sunni texts.

Also, the Qur'an says that God Himself threw the Shaytan (the devil) out of heaven. This is not to say that an angel could not have been involved; however, the Qur'an does portray it as being directly between God and Shaytan. It also implies that Shaytan accepted being thrown out insofar as Shaytan swore to misguide human beings until the end of time (and this oath implies that he is not trying to return to heaven).

Of course, God knows best!

A summary of what the angel Mika'il does as per Islamic texts can be found here: https://www.al-islam.org/ask/topics/4478/questions-about-Angel

The Qur'an mentions two types of prostration: (a) prostration as a form of worship and obedience (whether it be literal, as in during prayer; or figurative), and (b) prostration for reasons other than worship (for instance, in some cultures, it was/is a gesture of respect).

Qur'an 2:34, 17:16, and 20:116 say that Allah ordered Shaytan (Iblis) to prostrate to Adam. It literally says "to Adam", and I see no reason why it shouldn't be taken at face value rather than looking for a sideways interpretation. Obviously, Allah is not commanding Shaytan to worship Adam but rather it is a gesture of humility and an acknowledgment of the potential of the human being to ascend higher than the angels. It may also have been a test for Shaytan to prove his inner nature because, up until then, he had been seen as an excellent worshipper. 

(Maybe it was also a gesture of service, in that some of the angels, who were also ordered to prostrate to Adam, are assigned to serve people - for instance, in recording the deeds of people. Some people also hold it was out of reverence for the position of the Prophet Muhammad and his Ahl al-Bayt who would be born from Adam.) 

Anyway, all of this appears to have occurred outside the earthly realm. Some also say that "Adam" here refers to humanity as an archetype as a whole, as existing outside this world, and not the living, breathing human being. So, while we picture this as Shaytan getting onto his hands and knees and performing what we consider to be sajda to Adam as a human being, it may have been somewhat different. So for this reason also, it isn't really worthwhile to differentiate between "sajda to" or "sajda in front of". 

The Qur'an does not specifically say that sajda is only for Allah. Instead, it says that everything in the heavens and earth already does sadja to Allah, willingly or unwillingly (13:52, etc.). This can be taken to mean literal sajda as well as metaphorical. That is, all created beings are compelled to follow the divine decree and no created being can decide it is outside of Allah's control. Most creations willingly worship Allah, although human beings have the free will to worship Allah or other things (and we have the free will to perform sajda to Allah or not perform sajda to Allah). For this reason, the Qur'an tells people not to do sadja to the sun and the moon, and instead tells people to do sajda to Allah who is the creator of the sun and the moon.

However, according to Islamic law, it is not permissible for human beings to do sadja to other Allah. This is derived from Qur'an and hadith. 

According to the Qur'an and hadith, Shaytan is an immaterial entity who affects people through influencing their hearts and minds.

(By "immaterial", I mean that he is not composed of the same physical material as objects around us. The Qur'an and hadith say that humans are composed of earth, jinn of fire, and angels of light. The prevalent understanding from the Qur'an is that Shaytan is a jinn, although there is a minority view that he was created as an angel. So he is made of something, he is just not made of the same physical substances that we interact with.)

Qur'an 6:122 speaks of shayateen (those who serve the interests of Shaytan) who are humans and jinn. This indicates that human beings themselves can carry out the will of Shaytan without him actually being present in physical form. It also indicates that, when it comes to Shaytan and shayateen, there is a real division between human and non-human beings and it is not metaphorical.

In any case, from that, it is clear that Shaytan does not need to be here in human form to do the job. A commander who can send a footsoldier does not need to show up himself.

In fact, human beings do not even need Shaytan to cause evil! We have the capacity for immense good and immense evil on our own. 

There are some rare cases in the Qur'an where immaterial entities briefly appear as humans, such as when the angel Gabriel appears to the Virgin Mary, but it is not the norm.

Also, Allah protects the believers from Shaytan. 

So while there are some humans that I might identify as Shaytan (no names here!), the Qur'an lends itself to a more literal interpretation of Shaytan as a wholly non-human being rather than as a someone who is a human or walks around in human form.