I also often use Piano Adventures, but as a professional teacher I do always say... it's better with a teacher. It's actually easier to teach an intermediate-level student than a beginner-level. If you're competent on the piano but don't have pedagogy training or experience, I don't recommend teaching beginners... it's far too easy to 'screw them up' heh and create bad habits that later teachers then have to 'fix', for instance.
I know this is somewhat counter to the usual philosophy of homeschooling, that you don't need teacher training to be a homeschool 'teacher'. But piano -- like many arts and sports -- is a technical skill, not just general knowledge that can be 'absorbed'.
Beyond that, just because you know how to do it, doesn't mean you know how to break it down and explain it to a 6yo... or what to expect them to remember from one lesson to the next... or what practice ideas can be tailored to their particular strengths and weaknesses. That's where the experience of the qualified music teacher comes in.
For instance, I'd wager you'd try to teach your kid "Every Good Boy Deserves Fudge" (or Fruit) for the treble clef notes, since that's probably how you yourself learned it. Without going into the details as to why that's actually a really awful way to teach note-names (it's useful as a mnemonic, but NOT as a teaching/learning method), we have to stop and think about how meaningful an acronymic mnemonic would be to a 6yo who might not even really understand reading and phonics yet!
To be totally honest... if you're going to delay lessons for awhile, then don't try to teach him to read. He's still a little young for reading anyway... it would be very easy to try to do too much too soon and end up with bad habits like reading by finger numbers, or being stuck on only a few notes that he knows, etc etc. When I do have kids that age do note-reading, we do it very very slowly. Before we even get into notes, we first have to know the concepts of up and down (how the vertical on the page relates to the horizontal on the piano), of small steps and big skips, and of rhythm (shorts and longs). We do off-the-staff reading (usually just on the black keys) to learn these concepts before ever trying to learn the staff.
Skipping that would be kind of like trying to teach your kid to read words, before they've figured out that letters represent certain sounds. There's just certain concepts that kids are ready for developmentally at different ages -- like in reading words -- that you may or may not be aware of, and it can be frustrating not understanding why a child doesn't "get it". I certainly remember my first attempts, as a high-school student, at teaching beginners! I was like "this is C, this note here is C, it just IS... why don't you understand?" lol...
You'd be better off just letting him play on his own, or teaching him songs by ear, if you're going to delay lessons. You could teach him rhythmic note values... young kids can master that...
But I do recommend finding a qualified teacher -- again, that means someone with knowledge and experience with young kids, not just a new teacher, since like I said, teaching the beginners is the hardest level to teach! There is so much more to a music education than just reading notes! If you MUST delay for financial reasons, then don't worry too much about "teaching" him, just continue what you're doing with playing and singing... answer specific questions when he asks... and when he starts asking questions you don't know the answer to, say "would you like to take piano lessons to learn that?".