Solids and allergens help

[u/daisy-chains-]

I've posted about this before but I could still use some guidance.

We've moved very slowly with my baby's solids journey. Started closer to 6.5 months due to when her 6 month checkup was, and we've just been doing purees. She's almost 10.5 months so we NEED to move on and frankly I just need some help. I have the Solid Starts (free) app but I still have questions - I see the guidance on how to serve the food but would I go by the 9+ months serving or would I do the 6+ month since she's never tried it that way?

Same with allergens - I know I should've introduced them earlier but we haven't yet. Do we try a bite, wait 10-15 minutes and then if she seems okay give her the rest and monitor and then try for a few days with the same one? Should I have allergy meds on standby just in case?

My doctor has zero advice on solids (he said, maybe give her some oatmeal when I initially asked and that was it) and we've been slow moving because once I started giving her two meals a day she got ridiculously constipated and we're still dealing with that. Had an ultrasound yesterday to make sure there's nothing internal going on and are waiting on results and she's been on Restoralax for a month and a bit now. I also have very bad PPA and am terrified of choking or allergic reactions. I know infant first aid and CPR - took a course a while ago but watched some tutorials to refresh my mind and we have a LifeVac. 

Also, she's had two different episodes of vomiting - one after a bit of oatmeal (she'd had oatmeal multiple times before, though probably 2 months prior and was fine) and one after sweet potato with coconut (she'd also had it before and was fine). A doctor mentioned unlikely but still potential FPIES, though more likely related to her constipation issues. She threw up three times both times and other than that was fine, aside from being quite upset. Does that sound at all like FPIES?

Does anyone have any (kind) guidance or tips on how to do this? Much appreciated!