Will I have HD space for 2019?

I am currently running TANE, with the install on one 120 GB SSD with 96.2 GB free and the content on another 170ish GB SSD with 78 GB free. Thanks!

My TRS19 install folder is 16.5 Gb and user data space is 114Gb. There quite a few DLC assets in there but not a lot from the DLS.

Some of the DLC route packs are huge.

TRS19's base installation and bundled packages are quite a bit larger than the equivalent T:ANE Deluxe installation.
In my case, the program files occupy approx 13.4 Gb and my UserData folder takes up a further 78 Gb.
I don't download a lot of stuff from the DLS or elsewhere, preferring to create my own routes and sessions, but other people do, so your drive-space requirements ultimately depends upon your user habits.
In general, I would consider a 128Gb SSD too small for a basic installation of TRS19 as you need to provide some headroom for temporary files, and backups, etc. in the course of day to day operations - and SSDs perform badly when filled up with little free space available.
In particular, to take full advantage of the Trainz Plus Gold subscription offer, you should really consider a dedicated SSD (or available HDD space) of 256 Gb, or greater, IMO.

At this moment my folder sizes are:

TRS2019 103GB and growing
TANE 123GB
TS2012 167GB

All this is on Drive D, a 1TB SSD. Of course this will grow with updates to built-in and payware items which remain and cannot be deleted and so clutter up your drive.