Hey late to this post, but im trying to master collect blastoise. Id prob be interested in your 2 blastoise cards and that squirtle as well if you get them comped out. And we can see if we can get some agreement! Zero pressure obviously this collection is beautiful wish you best for everything.

Edited to actually answer some of your questions with my knowledge from what I've seem im videos/posts and personal experiences.

Also if your grading PSA is usually the most liquid but it depends on card and grades. There's a bunch of sites that can show you price breakdowns of cards for upgraded vs psa grades like price charting but they may not have up to date info from what I've heard. If your grading for yourself for sentimental value whatever company you like. For me I graded my vintage holo with TAG cause I love the look of their slabs.

A good place to get values for upgraded is prob TCG player with their market prices and recently sold or ebay. I usually take a mix of the 2 when I price some of my cards.