Hi Jim,
1/4 and 3/8 shank HSS tooling will work just fine on an Atlas. I would need to know more about your tool holders/tool post to be more specific. I would not spend a lot of money on tungsten tooling as an Atlas will really shine with HSS, and keeping the tools sharp and learning the tool geometry is probably more important at this point.
First thing I would do is invest in your education. There are several books on the subject.
Lindsay publications will have some if not all of them too.
http://www.lindsaybks.com/bks/lathebk/index.html
South Bend's is a classic. I highly recommend it.
Another Lindsay book I really like is Lorus J Milne's "Machine Shop Methods". It is a bit more modern than the South Bends ( not by much) and I think it reads well. He has plans in the book for some useful lathe attachments that would keep you busy too.
To get you started, I have attached a Lathe manual from a company called "Hercus". They made clones of the SouthBend and it's a decent book.....free too!
Atlas had a great lathe Manual and it should be available either on line or by ebay ect. It is very Germain to not only YOUR lathe, but other lathes in general and it will really lay a nice foundation of learning.
Of course, there is this forum and the incredible internet too. There is a lot of experience here on this forum. Ask away! Be a sponge! But I would get your head wrapped around a couple of good books.
The 10" Atlas can be a very capable and versatile lathe. I owned a late 1940's 10F for 10 years and I really loved it. I did tons with it and learned more!
Welcome!
Dave
View attachment Hercus TextBook of Turning.pdf