Win 7 all the way !
sorry
you dont need a huge internal drive but it should be an SSD, if it allows for a second internal get a larger sdd for that. I would avoid using this machine for any processing. period. the less "garbage" you have installed the better the machine will run and the less dropped frames you'll have. A 120or 160GB ssd is plenty for windows and your capture and control software. captures should always be to a separate drive (a large SSD) to avoid read/write delays causing control errors or dropped frames. do not record to a regular hdd if planetary/lunar/solar recording is what you want, the write speed will limit your frame rates which are important. you really dont want the OS tripping over itself by recording to the same drive everything it installed on , plus its easy to fill the drive. disable hibernation if you are going to use a single drive. record to an external usb3 ssd drive then just plug that into a separate machine to move for storage and processing then put empty ssd back on laptop for next imaging session. also best to make the laptop airgapped (no network at all, unless your control requires maybe plate solving on the fly i guess theres no reason. likewise dont have internet security garbage running at all times its just chewing resources and possibly hindering recording capabilities, you can use something that isn't autorunning that you can check the system periodically if you wish, but a standalone single purpose machine doesn't really need it. win 7 baby!