Extending an existing patio

I am a landscaping newbie and I am currently trying to extend an existing patio. I have a number of questions about how to go about this but first, I will do my best to describe the construction of the existing patio.

The pavers are a Stowell PCC 450mm x 450mm x 50mm utility paver. I have began digging around the existing patio but I am still unsure of the construction. It appears that the pavers may be laid on a screed grit sand, it is unclear if the grit sand is laid on top of a type 1 sub base, however there appears to be a concrete base underneath the patio roughly 200mm underneath the paver level. So far I have not discovered a haunch, or at least I haven't found a proper haunch.

Below are a couple of images, apologies neither are very clear. One image shows the pavers laid on what appears to be grit sand, the other shows an area I have started to dig, some excess type 1 (highlighted in red), a possible attempt a cement haunch (highlighted in yellow) and what appears to be a concrete base (highlighted in blue).

The questions I have are:

1. Can I use a 32mm paver rather than a 50mm paver to extend the existing patio, or would this cause problems for any reason. Stowell produce a 32mm version of the existing pavers, if I can use a 32 mm paver, it would save on cost and save my back.

2. Judging by my pictures, does the existing appear to be laid on a screed grit sand bedding layer?

3. I had planned to construct the new section of the patio with a type 1 sub base with a screed grit sand bedding layer. If the existing patio has a different construction, would this cause a problem?

4. If there is a concrete base underneath the patio, would this cause a problem?

5. Does the existing patio require a haunch? If I extend the patio using the construction detailed above, for which I plan on haunching the edges, should I try to haunch the existing patio on the edges that are not to be extended as well?

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