Hey Rebush,
I'm new to the site but own a Sherline 4400 lathe. Instead of buying Sherline's power feed I suggest making your own with a small DC motor/speed control. Sherline's PF is single speed, tends to overheat and is not reversible.
The Sherline lathe is like any other lathe; just smaller and capable of quite good precision. Therefore, you need a good QCTP, the Screwcutting setup, live center (ideally, make one with interchangeable tips), steady rest, follow rest, and a good 4-jaw chuck. Beall tools sells a really good ER-32 chuck to fit the Sherline and I use it a lot. I highly recommend making a rear-mounted parting tool holder for this lathe and buy a P1N parting tool. For the Sherline lathe, a 7 degree tool angle works well for a parting tool.
HSS tools work well on the Sherlline for fine work. Carbide works but not nearly as well because the speed, rigidity and power of the lathe is not well suited for those tools. I use 3/8" tools almost exclusively because the QCTP holders fit them well. Sharper than standard tool angles work better on a small lathe but that is a discussion for another time.
If you build engines you will need to bore. I suggest making your own boring tool holder for your QCTP. The one that comes with your set will not be rigid enough to avoid chatter in deeper bores. As you know, a clamping tool holder with a finely finished bore for the tool will reduce chatter to a minimum. If you need to use a boring bar larger than 3/8" then make a stand-alone holder from steel.
Make a good knurling tool when you can. The scissors type works far better than the Sherline one and is simple to make, since you already have a mill.
I also suggest making WR Smith's graver tool rest and gravers - it will take your work to another level. Just about every part that comes off my lathe is at least kissed with a graver to ease an edge or contour a part.Unless you need a precisely round part a graver is more versatile and often faster than a ball cutting tool for making rounded or ball-shaped parts. Highly recommended accessory.
I would consider a Walton guided spindle tapper (just a tap holder with a shaft coming out the back end) for this lathe. If you need to tap small parts this accessory helps to align the tap and keeps tap breakage to a minimum.
Hope this helps, and enjoy your new lathe!
Mikey