First/Last name begins & ends in the same letter…too rhymey?
Examples of what I mean: [name]Milo[/name] Manacito, [name]Caden[/name] Cannesson, [name]Harlow[/name] Hannacito
Would this be a no no in naming? Is it over the top rhymey?
There really are a lot of gray areas in the “rules” of naming so I think there are always exceptions. I find alliteration to be more often acceptable than rhyming or first and last names that end in the name sound. (Though I’m really not a fan of sibling names that all begin with the same letter). So with your examples for instance I would say [name]Milo[/name] Manacito and [name]Harlow[/name] Hannacito work, whereas [name]Caden[/name] Cannesson wouldn’t because they share many of the same sounds (both begin with [name]CA[/name], both end with an N). Does that make sense?
My name has alliteration (both start with the letter B, both have 2 syllables) and it’s never really been a problem for me. My name actually flows pretty well, and everyone always uses both my first and last name when addressing me (which I’ve grown to love, as nearly everyone I know does it and I never ask them to, they just… do). So while I am clearly biased, I think it’s fun and can be quite cute 
I second the above poster, though – it depends on the two names involved. You don’t want it to be too rhyme-y, then it looks made up or silly. But it can totally work - even to the name’s advantage.
In the examples you have above I do think they are too rhymey, alliterative, repetitive etc. Sometimes the same first letter of both first and last names can work but I am usually hesitant about it. I have heard it suggested that taking a letter from the last name (not the first letter) and making that a prominent letter in the first name can both deemphasize the last name and make the names flow well together. To use your examples of last names here are some first names that go with them:
[name]Carl[/name] Manacito
[name]Sydney[/name] Cannesson
[name]Oren[/name] Hannacito
Does that help?