The laptops are slow, cannot increase RAM. Either I improve drive performance with an SSD and a newer, safer OS ( Windows 10 ) or bypass it all with an Intel Compute Stick. If I use an Intel Compute stick, will it interface with my laptop's keyboard and monitor? Will it be able to communicate with the laptop's hard drive? What features will the Intel Compute Stick provide in this scenario?
Depending upon how old these laptops actually are, Windows 10 may or may not work cleanly on them. Intel does not provide graphics drivers for anything that is more than 6 years old (i.e. older than 3rd gen Core processor). Microsoft provides a compatibility driver that will allow it to work, but expect it to be slow and incompatible with modern DirectX, OpenGL, etc. applications.
An ICS, (a) won't interface with the laptop's keyboard or monitor, (b) won't communicate with the laptop's HDD and (c) really has absolutely nothing to do with these laptops.
You plug a dongle for a wireless keyboard/mouse into the ICS, plug the ICS into a HDMI input of a TV (and power) and then run it as a completely standalone computer system.
Hope this helps,