Stijn,
I'm afraid I'm not familiar with the TA152 but in general, most CL planes do not use down thrust. Out (or side) thrust is used in some cases to ensure tension on the lines. Unless you are flying in windy conditions or are using excessively long lines anywhere from zero to five degrees should be good. Remember, you are automatically causing pull on the lines when the plane trys to go straight.
Another thing is the rudder position. When CL first started, most thought that rudder offset was needed to keep it out on the lines. In most cases rudder offset is not needed.
You might find that many use engine and rudder offset as insurance so if it it makes you feel better, by all means use it.

Tank: Unless you want to duplicate the old one, a modern plastic RC tank should work...if it fits. They can be plumbed for CL use.

Good luck with your TA152.

George