Yes, too high a grit and you burnish the surface, close up the pores and stain take-up can become very patchy. In general you really don't need to go higher than 180 grit before staining, though sometimes using a higher grit on just the end grain sections can stop those from taking up more stain and becoming darker than the rest of the body. The higher grits get used on the finish.
I haven't used it yet, but you can get a pre-stain conditioner than seems to get good results and evens out the stain absorption, reducing excessive end-grain take-up. No idea what people have used on here but a web search throws up a few hits.
Based on your posts above I have the plan as follows. Can I chack I have not mis understood you please?
Check for glue by using a damp rag then clean glue off using goo off and light sanding - at this stage it appears only to be on the sides and not the front.
Front and sides - sand to 180g
Grain fill with timber mate slurry on sides and back
Sand back and sides starting at 320. Repeat grain fill and sand if required
Stain sides and back after masking front and binding
Front and sides - x5 coats of the Tru Oil working in small circles front, back and sides. 3 coats per day max. Followed by 600g light sand on back and sides only not front(total 15 coats)
Front and sides - x5 coats of the Tru Oil working in small circles front, back and sides. 3 coats per day max. Followed by 1200g light sand on back and sides only not front(total 15 coats)
Cure 3-4 weeks
Front - Polish front
Back and sides - light sand with synthetic sanding pads for satin finish - satin varnish as a fall back