You don't mention what you struggle with but, in general, I say:
I've been recommending this book all day: https://www.amazon.com/dp/1563674505/ref=cm_sw_em_r_mt_dp_ySAIFbWX40FKA
The author used to teach sewing at FIDM and this book is based on her course.
Get a Vogue, Singer, Burda or Alison Smith sewing book or similar.
Burda Style has stars next to projects to indicate difficulty levels. Why not use that as a guide and make up similar patterns you own, to build your skills?
YouTubers I recommend: Evelyn Wood, Fashion Sewing Blog TV and Lifting Pins and Needles.
Good luck!
1) Older machines have a good reputation, generally, because they tend to be more metal than plastic the older they are. Do you have the manual?
2) If you don't want to take your machine to a professional, here's a helpful video: https://youtu.be/FmfWu83I0ZI
3) I always recommend in-person classes. I'm assuming you're in the US? In any case, look around you, fabric stores, community colleges, sewing lounges, all offer beginner sewing classes.
If that is not possible, a good vlog is Colleen G. Lea of FBSTV channel. Unfortunately, her playlists are not the best so look around, she even teaches how to thread a needle!!! https://www.youtube.com/user/FashionSewingBlogTV/videos
Also: https://mccallpattern.mccall.com/collection/learn-sew-fun US sleeve patterns go on sale regularly at chain stores like Joann's and Hobby Lobby. Since it's Thanksgiving, I susptect there is a $2 sale going on right now.
As a rule, you need to a) know how to use your sewing machine b) know how to sew straight seams and c) know how to sew curved seams. The rest is variations on those skills.
If you intend to sew clothing for yourself, see if you can borrow this book from the library, it's supposed to be based on the curriculum of a Fancy Design School: https://www.amazon.com/Guide-Fashion-Sewing-4th/dp/1563674505/ref=nav_signin?crid=ZYH8KIICFOAN&keywords=connie+crawford+books&qid=1574865107&sprefix=connie+crawfor%2Caps%2C165&sr=8-2& (sorry, couldn't get the shorter link to work).
You will also need a good reference book like this one: https://www.amazon.com/dp/1606522086/ref=cm_sw_em_r_mt_dp_U_NMO3Db0YYHHR5