I think going to a good shop with patient and experienced employees is the best thing you can do at the outset. Later you can start buying online (SidelineSwap is AWESOME). I find that I spend an average of an hour fitting players for protective gear if they need multiple items. My recommendation is not to lock yourself into any one brand and choose with your eyes closed. There's always a mobility/protection trade-off, but if you're patient, you don't have to give up too much of either. I would take all the marketing with a grain of salt. For example CCM markets Jetspeed as mobile and Tacks as protective. FT6 Pro pants are more protective (IMO) than AS-V Pros. It's more important that your gear fits properly and accommodates your individual mechanics than what the catalog says. Try as many brands and families as you can and put together a package that works for you.
When I have kids that I coach who come with stuff that's not right for them. Often they've made decisions with their eyes. They got what they thought looked cool, or it's what Connor uses, or the coach said to get it, or the blurb online was convincing. All that matters is that it fits you correctly and works with your mechanics.
Anyway...that's my opinion. Good luck!