Karabiner Elements still doesn't have the chording needed to emulate TB.
That said, the default macOS keyboard files are also quite clever, although they don't support timing-based events. What you can do is go into a different state upon keypress, and in that different state you can emit different things. So making space a combo key is probably doable, but it will be unforgiving regarding timing. If you release the space a fraction too late before hitting the next key, you will be sending green layer keys.
For Edit mode, you need to let D and F go into special states that send all keys as normal, except when also pressing F or D, in which case you go into edit mode (state) until both are released.
http://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&id=ukelele is a good editor for these files.
The hairy thing about the TB layout is getting the chord timing to be intuitive, and this won't do that, but it's a beginning.