First generation, Factory Sealed IPad Pro, 9.5" , 128 GB - resell value ?

Normally yes. Sealed items will be worth more. Check completed auction son ebay for the amounts people have actually paid for a seal iPad Pro vs an opened one. I found around $200USD difference in a cursory look.

Apple Pencils that have not been used for an extended period of time tend to have their battery fail, since its very small and can easily perish. You'll find sealed pencils will be dead when taken out and likely returned for a full refund.

Not worth it in my opinion.

A first generation iPad Pro cannot be updated beyond iPadOS 16.7.x. iPadOS 17 is current - and will itself soon be superseded for compatible devices by iPadOS 18. For this reason alone, with Apps becoming increasingly incompatible with older models, the potential usefulness (and hence potential value) will be increasingly limited.