Find a local builder and discuss your needs face to face. It needn't be over expensive doing this and you will have a machine built to what you want rather than an off-the-shelf item of what someone thinks you want.
Don't go for the latest or fastest this or that.
Do go for the second (or less) fastest CPU etc. - the one that has just been superseded by something faster - you will find that is much cheaper. Super speed is not what is required for your end uses - plenty of space is.
For preference have two hard drives - one for O/S and programs the other for files.
Always ensure you have a backup of your work.