Everyone is probably saying this already but Hooked By Robin is THE BEST. If it's a repeat endorsement, just take it as compounding, because she's honestly the absolute best. She goes slow, explains every stitch, and she's got everything from scarf patterns to decor stuff to amigurumi. She's *so* good.
Like a few others have suggested: 5mm hook and standard DK/WW yarn. This is what most standard projects use (blankets, clothes, a lot of amigurumi) use. I have had very few projects I've done require anything different. It's also just a really nice size to work with. Not so small that its frustrating, but not so big that it causes hand cramps.
My first suggestion would be just a simple granny square blanket, but not making a bunch of granny squares and stitching them together, literally an ever-expanding single granny square. It teaches you SO much about stitch tension, how to check your own work for errors, and it works up really, really quickly compared to something more solid. Plus, I find that working "in the round" (sort of, in the case of a square) to be a wonderful learning experience.
Also learn how to work in the round properly. There are youtube tutorials for how to make cute little round "dish scrubbies" or dishpads or whatever. Thats what I started out making and I absolutely learned a ton.
OH! And I know there are probably a lot of people who will disagree, but I found that buying a pack of stitch markers (they look like this) made my life so much easier. I know there are ways you can use little chopped up pieces of yarn or a running stitch marker, but I have never found those particularly easy to fuss with and I'd accidentally knock 'em out all the time!
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Welcome to the club!!
Here’s the set of crochet hooks i currently use for all my projects crochet beginners set It has everything in it you need to get started besides a pair of scissors.
Amazon! I was able to get a bunch at a decent price 50 Pcs DIY Black Plastic Doll Teddy Bear Safety Eyes with Washers(30 MM) https://www.amazon.com/dp/B07BCD9HJJ/ref=cm_sw_r_cp_api_fabc_fL.XFbS22BJP2?_encoding=UTF8&psc=1
First, I support Michaels and will never recommend hobby lobby.
But. I would personally recommend Amazon for this as I never found anything similar in my Michaels when I started a few years ago.
My hooks weren't very expensive - hook selection is a matter of personal preference. You might want to buy a few single hooks from different brands, until you know which you prefer.
I recently bought a cheapish hook set with case and various accessories on Amazon, that I really like. https://www.amazon.com/dp/B08R1QSJQX?ref=ppx_yo2_dt_b_product_details&th=1
The great thing about crochet, is that all you really need are some hooks and some yarn, stitch markers and plastic needles to weave in your ends.
She did such a great job! If you look on Amazon you can find tons of great “Amigurumi” (crochet stuffed animals/dolls) such as this Fanatsy Amigurumi and you should check out free patterns on Raverly. She’s got a lot of talent and she’d probably enjoy more challenges during quarantine/social distancing. Thanks for supporting her creativeness!
If you don't mind which colors you get, there are some good value mystery packs on Amazon like this one. I have ordered this 3 times in the past and the range of colors varies a lot. It's hit and miss but as you need so many colors it may help. I think they are the weight you are looking for. https://www.amazon.com/gp/product/B07B434G64/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1