Any pointers/advice for starting CUL?

[Mirarara]

This certainly isn't true. Culinarian is my only level 70 craft and I got there without using a single cross-job skill. Having botanist and taking the time to gather your own materials is, however, very useful.

You can get to 70 without cross class skill, that's for sure. But it will be extremely difficult to 100% HQ 66+ stuff (which I supposed it's his intention) without cross class skill or heavily melded lv 70 eq.

Edit: I supposed it's still doable but I don't think most people would want to solve a puzzle of 100% HQ for high level recipe without cross class skill such as byregot blessing, piece by piece, ingenuity and careful synthesis II. If they like this challenge they won't even ask how to in the first place.

Edit2: As stated by OP, he wanted to craft Jellied Compote, a lv 70 1 star recipe. Cross class skill is almost certainly needed.

Edit3: Also, I find levelling from 50 to 70 much less expensive if you have the required cross class skill, due to how you can craft your own leve item or collectible easily. While I have my own gathering at max level, I never gathered my own item to level CUL because it take much lesser time to just buy from marketboard, and sell the crafted item at around the same price. You just need to do some research on the MB.