Secure openSSL file encryption - powershell

Question

I wish to encrypt gigabytes of data with OpenSSL (multiple files), securely.
I use this command (openSSL 1.0.2p-i386-win32):
openssl.exe enc -e -aes-256-ctr -in secret.txt -out encrypted.txt -salt -pass pass:AsIDHnd19!&###!#lJglG1f31!
My questions are:
What mode to use? CTR or CBC? (CTR for speed?)
How to generate random IVs? For example in a PowerShell script. (I am using Pshell v2.0)
Is the command I provided secure enough?
Can I use the same salt for every file, for better encryption speed?
Does a 20-30 char truly random password compensate for the lack of
IV?
EDIT:
I downloaded a newer version, with ability to use PBKDF2 (openSSL 1.1.1-win32-mingw):
openssl.exe enc -e -aes-256-ctr -in secret.txt -out encrypted.txt -salt -pass pass:AsIDHnd19!&###!#lJglG1f31! -pbkdf2 -p
With -p I can see the salt, key and IV that's used to encrypt the file. All 3 parameters change every time I run openssl, even if on the same file and with the same pass.
Does that mean I'm safe now and IV is random?

Answer 1

CBC and CTR should have same speed around.
If not specified IV is generated from your password with pbkdf2.
CTR is recommended to CBC.
Using the same salt is not adviced. Salt used to prevent attacks for the password, from OpenSSL documentation.
Without the -salt option it is possible to perform efficient dictionary attacks on the password and to attack stream cipher encrypted data. The reason for this is that without the salt the same password always generates the same encryption key. When the salt is being used the first eight bytes of the encrypted data are reserved for the salt: it is generated at random when encrypting a file and read from the encrypted file when it is decrypted.
IV is not lack of. OpenSLL generates is for you if not given.