The structure of this perek is unusual. It's long, and there's a lot in it.
12:1-2 consist of a command from Hashem regarding calendrical structure, declaring Nissan to be the first month.
12:3-11 contain details of the first Korban Pesach, made by the Hebrews in Egypt. Many of the specific commandments regarding its procedure continued to apply for the Korban Pesach L'Dorot.
12:12-13 contain a brief digression in which Hashem describes the harsh final plague He intends to bring upon Egypt, and how the homes of the Hebrews will be passed over (provided the blood of the Korban Pesach is on their doors).
12:14-20 further develop the concept of the Pesach holiday and the commandment to eat matzot.
In 12:21-24, Moshe relays Hashem's commadments about Pesach to the nation, as well as the warning to smear the Korban's blood on their doorposts. Immediately following this, in 12:25-28, Moshe explains that this holiday is meant l'dorot, and emphasizes the importance of teaching one's children about it.
12:29-36 is a reasonably straightforward narrative that describes Hashem's execution of the Plague of the Firstborn, Pharaoh's panic, and the hasty departure of the Hebrews- after they take all of Egypt's valuables. In 12:37-39, the beginning of their desert journey is recounted, and in 12:40-42 the duration of the Egyptian exile is expressed explicitly.
12:43-50 make an odd return to discussing further laws of the Korban Pesach, including who may and may not eat from it and the laws of the proselyte as regards the Korban. 12:51 concludes the perek with a final mention of Hashem's taking the Israelites out of Egypt "on that very day".
There seems to be a contrast created between the immediacy of the event at the time, when it was unfolding, and the fact that it would be an event memorialized for all time. All the speech in this perek seems to play on this duality of the Exodus being a historically important event that was still in the process of occurring. This juxtaposition creates a perek that serves two purposes: it is a narrative, in the same vein as the first eleven perakim of Sefer Shemot, but it is the first part of the narrative with technical, practical repercussions for the Jews l'dorot. A comparison I can think of is the interjection of the l'dorot mitzva of gid hanasheh into the narrative of Ya'akov fighting the angel.
Ibn Ezra makes a number of comments important to understanding the nature of Pesach as a command that was both immediately and generationally relevant. In Pasuk 11, Hashem says that the Hebrews shall eat the Pesach with their belongings packed and in full travel garb, prepared to leave Egypt swiftly. Ibn Ezra comments there that that command achieved its full potency in Egypt, and that the command to eat it roasted fits in with that idea of efficiency and swiftness, as roasting is a very fast way to cook meat. These practical concerns obviously don't have too much bearing on future Pesachs, which may be why the pasuk in Devarim 16 uses the word "bishul", or cooking. (Although the l'dorot mitzva does wind up being to eat it roasted.) Ibn Ezra on 12:24 explains that though some think that the commandment to smear the lamb's blood on the doorposts is l'dorot, we have a tradition which tells us otherwise. The word "hadavar" in 12:24, he says, refers to the early command to eat the Pesach in general, and not to the immediately preceding doorpost smearing command. The unique way in which the Pesach is eaten, with care not to break bones and joined by a chaburah, is unusual enough as to elicit questions from one's children as per the pesukim here. Ibn Ezra explains (12:43) why the laws of geirim and slaves are interjected at the end of Perek 12. Since it immediately follows the declaration of Pesach as a "leil shimurim", the perek concludes with the balance of the laws of Pesach that hadn't been previously mentioned- that is to say, those which are only applicable l'dorot and had little relevance in Egypt. The concept of owning slaves to circumcise and with whom to share the Pesach must have sounded incredibly foreign to the slave nation of the Hebrews. The first part of Perek 12 is dedicated to those laws which were relevant for Pesach Mitzrayim, including some which were only relevant then (smearing the blood, etc) and some which were l'dorot. The end of the Perek, in keeping with the narrative's awareness of the historicity of the events therein, lists the remaining laws that would pertain to all future Pesachs.
When it comes to how the Pesach ought to be cooked, there's a profound distinction between Shemot 12 and Devarim 16. In Devarim, it says that the Pesach ought to come from "cattle or flock", "bakar" or "tzon", while Shemot specifies a "seh", a Hebrew word for young sheep or goat with no English equivalent. Devarim says it should be cooked (bishul), while Shemot specifically says not to do this and that it should instead be roasted over flame. The Malbim explains that this doesn't exclude cooked recipes for the meat of the Pesach, but that it must first be roasted if one wants to cook it in another way. It must go from raw to roasted, and then it may be prepared by cooking. Perhaps this is hinted to by the use of "bishul" in Devarim.
1. The Exodus was the beginning of a process that conferred nationhood on the Israelites; the calendar reform was one of their most basic rights as a nation.
6. This is a famous question regarding the chronology of the Egyptian exile. Considering the lifespans of the early Israelites, and the fact that Moshe was 80 at the time of the Exodus, 430 years seems like a vast overestimate. Most of the commentators agree that the 430 years was counted from the Brit Bein Ha'Betarim, at which Avraham was told his children would be in exile for 400 years; Yitzchak was born 30 years later so that the count of 400 years is accurate from the time that Avraham had a child whose progeny were destined for the exile.