Hey @TorqueMonster1 Welcome to the forum! Were are happy to have you! Great questions.
Ive been doing automotive and marine upholstery for a long time now and what I use %90+ of the time is size 92 UV protected bonded polyester. The only reason I use a thread bigger than size 92 is for aesthetics on a decorative top stitch. For the projects your talking about sewing there are really no reasons you would ever need a bigger thread than 92. You would even be fine with size 69. I use and recommend 92 because its easy to find and most supply stores in the most amount of colors.
I will usually use the same size thread in bobbin as what I'm using in the top. If I go above size 92 on the top thread I will usually still use size 92 in the bobbin. Because like I said above 92 is for looks not strength and by keeping 92 in the bobbin you can sew longer.
As far as the science goes... I think people complicate it way more than it needs to be. Bottom line you want your thread to be stronger than the fabric. Size 92 poly is WAYYYY stronger than any material you will use in auto / marine. If it will be in the sun you want UV bonded polyester if it will be inside you can use nylon but I still use polyester because I don't want to have both laying around.
For useful sites. Here is already a great start your welcome to ask any questions you have. Our goal is to build the best online resource for upholstery and every question helps. Our other site TheluckyNeedle.com has a lot of great information. Our YouTube channel has a bunch of how to videos https://www.youtube.com/user/TheLuckyNeedle https://www.sailrite.com/
has a lot of info I dont want to discount The Hog Ring http://www.thehogring.com
because they really do have a lot of good info but they don't welcome beginners
For needle size watch this video.
and here are some guide lines for thread and needle size
Size 15 / Tex 16 / Govt. 00 - Use needle sizes 70 / 10 to 80 / 12
Size 33 / Tex 35 / Govt. AA - Use needle sizes 80 / 12 to 90 / 14
Size 46 / Tex 45 / Govt. B - Use needle sizes 90 / 14 to 100/ 16
Size 69 / Tex 70 / Govt. E - Use needle sizes 100 / 16 to 110 / 18
Size 92 / Tex 90 / Govt. F - Use needle sizes 110 / 18 to 125 / 20
Size 138 / Tex 135 / Govt. FF - Use needle sizes 120 / 19 to 140 / 22
Size 207 / Tex 210 / Govt. 3-Cord - Use needle sizes 140 / 22 to 180 / 24
Size 277 / Tex 270 / Govt. 4-Cord - Use needle sizes 180 / 24 to 230 / 26
Size 346 / Tex 350 / Govt. 5-Cord - Use needle sizes 230 / 26 to 280 / 28
Size 415 / Tex 410 / Govt. 6-Cord - Use needle sizes 280 / 28 to 330 / 30
Size 554 / Tex 600 / Govt. 8-Cord - Use needle sizes 330 / 30 to 360 / 32
I got this from here. http://www.thethreadexchange.com/miva/m ... creen=CTGY
Sounds like you have a great machine! very similar to my Juki lu-562
@torriec work for Albrights supply https://www.AlbrightsSupply.com/?Click=3957
a great online store for upholstery supplies and full of knowledge!
@Trimjobber owns Bry-tech distributors another good supplier and full of knowledge.
As far as brands go I have always used COATS bonded polyester. Amann Serabond Thread is supposed to be even better. There is some info here. Amann Serabond Thread - Is it really that good???
This video will hopefully help also
No worries on not being up to date on the internet stuff! I did a little video that goes over how to use the forum here.
How To Use The Forum and Its Features
I hope this helps answer some of your questions. Most of all don't be to afraid to just jump in and try things. The most important thing is jumping in and learning and getting comfortable sewing and using the tools. You'll learn the rest along the way.
@BigRig Great info and answers as well!