sentences are ok except that you don't translate "on" by "sur" at the end of the phrase.
so it's je peux vous appeler plus tard, et je vous appellerai plus tard.
yes, peut-être is perhaps or maybe. so the translations are:
1- pourrais-je vous appeler demain? (peux-je doesn't exist)
2- pourrais-je vous appeler plus tard?
3- puis-je vous appeler demain?
4-puis-je vous appeler plus tard?
but, ideally, we will use easier "est-ce je pourrais vous appeler, ou, est-ce que je peux vous appeler".
It is less formal.
However, don't abuse of the "sur" word. If you want to literally translate "for sure", use "à coup sûr", as in "Je vous appellerai plus tard, à coup sûr". Although in this case, "Je vous appellerai plus tard, c'est promis" (you make a promise) would sound more natural.
"Je peux" means that you might or that you can, not that you will. So it's not 100% sure. So don't add "sure" or anything that would mean the same thing.
Frank -- in this case, the word sur was a confusion with the English word on.
In English, it's commn to add certain prepositions to emphasis a particular notion that don't actually carry much meaning per se and aren't always translated. So here, on emphasises "continuation" from the present time, but essentially later on means "later" and the difference is too subtle to usually bother trying to render. (Maybe later on is closer to un peu plus tard, but it's really arguable.)
Another case that crops up is with some verbs of motion, where it's common to encode direction as a preposition in English, but in French the direction is either not encoded at all, or encoded in the choice of verb. For example, it's common in English to say, for example, I'm going up to Scotland for the weekend, they came over from Manchester, I'll be down in Wales. In these cases, it doesn't always add very much to try and translate the preposition. For example, you could say e.g. ils sont venus de Manchester en passant par la montagne if you're desparate to translate the notion of "over", but really the essential meaning is ils sont venus de Manchester.