I don’t think I have much to add to what others have already said. You’re quite a bit off in quite a few places, especially on page 7. Some of it is gonna be what other pointed out already:
That’s a ひ, not an い, but yes that’s does mean “it’s been a while” - one thing though, な is just ね, and ひさしぶり is a noun (or a na-adjective, same thing really), so ひさしぶりだ is one thing, だな is not a separate addition to it. This is really just “it’s been a while” with ね basically asking the listener’s agreement (which doesn’t have to be explicitly stated, you don’t actually need to confirm everything marked by ね, it’s more intended to convey that you presume the listener agrees and/or what you’re saying isn’t new to them) - so something like “it’s been a while, hasn’t it?”
As already stated, おーー is just “oooooh”, not the honorific prefix. You generally wouldn’t use the honorific prefix for people’s names anyway, there’s honorific suffixes for that (さん, さま, etc.)
Just the sound effect of a hand being placed on Yotsuba’s head
Not sure why you separated this in this way - 元気にしてたか is one sentence - “have you been well?”
That’s うあー - just an excalamation, basically “whaaaa”
Yanda is a different person
And that means he’s implicitly the subject of this - Yotsuba’s dad is asking if he’s not here yet
This one’s also one sentence. You’re paying too much attention to line breaks, really - a sentence can be split over multiple lines, just like in normal written text.
あいつ用が入ったからこねえって is the full sentence. あー is just “ah”.
あいつ is a colloquial/familiar (and sometimes disrespectful) way of referring to someone. Think of it as an informal form of あの人. There’s also こいつ, そいつ and どいつ which are basically the colloquial この人, その人 and どの人 (but more in the sense of “who” than in the sense of “which person”) though I don’t think I’ve ever seen そいつ or どいつ used.
こねえ is こない, あい can become ええ in some contexts (usually in very casual speech), like with うるせえ being the same as うるさい. って is once again a quotation marker, から marks the preceding (あいつ用が入った) as the reason for こねえって.
So: he said he wouldn’t come (こねえって) because (から) he had things to do (あいつ用が入った)
This is basically nitpicking since the transcription is accurate, but a more natural way of transcribing this nickname would probably be Jumbo. Probably because he’s a full head taller than Yotsuba’s dad 
This is one sentence split over multiple lines as before, with a misreading as pointed out by others:
しばらく見ないうちにまた大きくなった
うちに is a grammar point you haven’t encountered before, and just means “while” (as in “during the time in which the previous bit took place”).
大きくなった is also a general pattern you’ll see a lot, replacing the い for an i-adjective with く makes it into an adverb, and [adverb form of adjective]なる just means “to become (more) [adjective]”. 大きくなった means “you got big” (or “you got bigger”). しばらく見ないうちに marks the timespan for that, so she’s saying “you got big while I didn’t see you for a while” (or more naturally “you got big since I last saw you”) - she’s mimicking the people who say that to her every time, as people tend to do with kids 
I think a big part of your misunderstanding here is you’re splitting a sentence again because it’s over multiple lines. It’s one sentence (and you have a typo - that ば is a ぼ): お？どこでおぼえたそのセリフ
どこ is just “where”, で marks it as a location for the verb, which is おぼえた (to learn - by memorisation, not by being taught). セリフ is a bit of a tricky one to translate, but it can refer to anything spoken, basically. Stories, words, phrases, comments, remarks, etc.
He’s asking her where she picked up the phrase she said (しばらく見ないうちに大きくなった) since it’s clearly something she’s just mimicking off someone.
まあいいか does happen to be a separate part of the sentence, so you got that more or less right. It’s basically just a “filler phrase” he uses to say “I think we’ll manage” (though literally he makes it a question but I guess that’s more so to soften it, in a way)
The latter part of it is once again a single sentence: ジャンボが二人分働くしな
し is something you haven’t encountered yet, and marks a reason for something. You’ll often see this when listing multiple reasons for something (目が大きいし頭が丸いしその猫が可愛い - that cat is cute because its eyes are big and its head is round) but you can also see it used like this for a single reason.
な is once again just ね
二人分 means “two people’s share” (or “a portion for two”)
So he’s explaining why they’ll manage - it’s because Jumbo will do the work of two people.
You’ve got the gist, but keep in mind that Japanese doesn’t really have a present tense, just a non-past tense, so ない can be present or future tense. This is more “that won’t happen” than “that never happens” - but “never!” or “no way!” covers it nicely.
Notice the negation: he’s saying “I won’t work”
働いて is just the て-form (conjunctive form) of 働く, linking it to the くれ you missed here (which is a colloquial form of ください, essentially). He’s saying “please work”
That’s とーちゃん, not うーちゃん - he’s saying “your dad’s useless”
That’s said by Yotsuba, not her dad - she’s repeating Jumbo’s とーちゃんはダメだ
I hope that helps! In general just try to see where sentence boundaries are. Most of the time they’ll be marked by either punctuation or the end of the text balloon, but line breaks can happen mid-sentence. Keep that in mind, I think that’s where a lot of your misinterpretations/mistranslations come from.
I’m super impressed that you could make it out! Hmm it’s a little too small for movie popcorn