You have to have paper and/or cardstock but I would take your photos to the store and match what you want. Don't start buying everything because you don't yet know what you are going to really enjoy and use.
Adhesive. No way would I use a glue stick on my pages - I know people that do but not me. I've seen lots of scrapbooks with crinkled pages from gluesticks. And I don't think they hold up over time very well. ATG is my adhesive of choice but I started out using the inexpensive tape runners. Those get expensive however if you do a lot of scrappbooking for the first scrapbook or two they are fine.
Beyond that, buy what you like. If you want to handwrite your journaling, buy journaling pens. If you don't plan to handwrite your journaling (I do mine on computer so don't need pens), or some people don't journal at all. In that case, you don't need pens.
If you want to use stamps on your pages, buy some. If you don't plan to stamp your pages, don't spend your money on them.
Beyond the paper and adhesive - a good trimmer is necessary. Go to a scrapbook store and ask if you can try out several to see which is best for you. I swear by the Fiskar's rotary but others like the guillitine which doesn't work for me. Others love the little wire trimmers. I don't know that any are really "best" - its a matter of which is best for you. You will only know that when you try several.
You may want to buy sticker letters for titles - unless you have a lot of money up front to spend on cutting machines.
Mostly, go through the gallery and see what you like and then buy embellies and products to go with your page.
Don't buy pens unless you know you are going to use them. I bought several 5 years ago - never took the cap off any of them. Don't buy stamps unless you know you are going to use them. Same with buttons and ribbons and brads. If they are on the pages you like and you keep being drawn to pages with those items, then you will probably use them.
Some people love sketches. I have one sketch that Kory designed for me and I am definitely going to use that one, but as a general rule, I don't like using sketches. I'd rather go by something I pulled out of the gallery and can see how it actually looks on paper.
The first thing I did was go through the gallery and copied layouts I like into a file on my computer. It has several hundred layouts in it now and I refer to it all the time for ideas to get me started. I rarely scraplift one completely, mostly I use them just to get going and for inspiration.
A mistake I made was copying layouts with no note of who the artist was and later when I did "life" it I didn't know who to credit. Now when I copy someone's layout into my file I rename it with the artist and the name of the layout from the gallery so I know who to credit. I wish I had done that from the very beginning becuase I feel guilty getting ideas from artists and don't credit them.