Will i need to use winbind and kerberos?

Most likely not. The Samba fileserver provides the same features regardless of where the accounts come from – your local Samba accounts are already automatically associated with the corresponding OS accounts, etc.

(However, Active Directory would be a good idea if you have more than 3-4 servers.)

Who should be the owner of the shared folders?

Doesn't really matter; root would be a good choice if there's no specific owner otherwise.

If set create mask, directory mask to 755 do i have to change the directory permission with chmod?

Depends on situation, but most likely "yes".

Samba's "create/directory mask" settings do not change existing permissions; they only specify what will be used for new files created on that share. If you want to make a public share but the directory currently has permissions 0700 – Samba won't change that; you have to chmod it yourself.

Will the 755 permission work or is should change?

It's the standard "readable by others" permission. It doesn't really match your descriptions though – for home directories it'd grant too much (unnecessary 'read/execute' for others); for shared directories it'd grant too little (missing 'write' for others); so you probably need to change it in both cases.

If someone downloads a file via transmission can the user be the owner instead of transmission?

Only if the users run their own Transmission instances (each on its own port number).

As Transmission is a local process, it is unaffected by SMB server configuration – all files it creates will be owned by the account that Transmission itself runs as.

Disable the system-wide Transmission service, then create a "user-level" transmission.service in /etc/systemd/user/, which each user could start using systemctl --user. (There are some differences in what settings to use, but those are already documented elsewhere.)

Don't forget to use loginctl enable-linger to allow the users' personal services start on boot (by default they're limited to login—logout, but the "linger" mode avoids that).

Edit the samba configuration file.

sudo nano /etc/samba/smb.conf

Add this to the end of the file:

[Public Directory]
comment = Contents are read/write by all.
path = /home/user/directory-to-be-shared
read only = no
guest ok = yes
create mask = 0666
force create mode = 0666
directory mask = 0777
force directory mode = 0777

Then restart samba.

sudo service smbd restart

Notes:

1. The string within brackets (Public Directory in the example above) is what users will see when accessing the shared folder from other systems.
2. Files created within this directory by users on other systems will be owned by nobody:nogroup, with read and write permissions for owner, group, and other.
3. Directories created in this directory by users on other systems will be owned by nobody:nogroup, with read, write, and directory traversal permissions for owner, group, and other.
4. The masks and modes in the configuration file apply to files and directories created by users on other systems. These masks and modes are ignored when creating files as a user on the server. Or, to put it another way, if you are user on the server, make sure that each file and directory that you create within /home/user/directory-to-be-shared has 666 and 777 permissions respectively.

5. If you have enabled a firewall on the server, you will need to open port 445 for tcp. For example, if you use ufw (uncomplicated firewall) to configure the firewall:

   sudo ufw allow in 445/tcp
   sudo ufw reload
   sudo ufw status verbose
   

I recommend to create a dedicated user for that share and specify it in force user(see docs).

Create a user (shareuser for example) and set the owner of everything in the share folder to that user:

adduser --system shareuser
chown -R shareuser /path/to/share

Then add force user and permission mask settings in smb.conf:

[myshare]
path = /path/to/share
writeable = yes
browseable = yes
public = yes
create mask = 0644
directory mask = 0755
force user = shareuser

Note that guest ok is a synonym for public.

Let's take just the first share as an example - and here I'm correcting the read-only = yes line:

[Fr-data]
path = /free/fr/data
read only = yes
valid users = @global
write list = borhacker
force create mode = 0775
force directory mode = 0775
create mask = 0775
directory mask = 0775

The only user that will gain access to the folder being shared is borhacker. Not becase of the share definition in smb.conf but becase the parent folder only allows that user access. In fact borhacker is the only user that can access any of these shares for the same reason.

This represents the Linux permissions on /free/fr:

drwxrwx--- 15 borhacker borhacker 15 Dec 19 12:39 .

You need to allow users other than borhacker the ability to traverse the /free/fr folder:

sudo chmod 775 /free/fr

A samba share definition cannot override the Linux permissions of the folder being shared or the Linux permissions of the path to that folder