Is there any Voice/talk program to set up at KDE start to give you a welcome?

never heard of one but you could:

- create a script that plays a "welcome" sound file and place it in the autostart folder. You can use the command play to play the file to skip having a player load.

- use Kalarm's built in audio alarm to play a "welcome" sound file using the anytime option. This will not play till KDE and Kalarm are loaded.

I believe Kttsd / Jovie can do this. Open System Settings > Application & System Notifications > Applications. From the drop down "Event source" select "KDE Workspace". Enable "Speech", selecting "Speak custom text" and enter the desired text.