Let me weigh in as an instructor of new students.

The OP wants a LT40. That is a great choice. A 46 is plenty of power. I have trained students with heavy Mark II's with 35's that flew well.

Second he has run cars so he is familiar with the controls being reversed coming at him. (that is half the battle with new students.)

A multi engine plane can be flown easily on four channels if he does not need flaps or retracts. So a six channel is more than enough radio for most planes. He is already invested in spektrum though I am not a fan of them. it is good to stay with what you know or are familiar with.

My recommendations for success.

Build the plane by the plans. Use epoxy on the firewall and other critical areas. (Wing half join, tail section, etc.) Removal of half the dihedral in the wing will help with basic aerobatics. (if desired.)

Get HELP! Find a local club and go there. They can test fly your plane and make sure it is set up properly. They should have instructors that will teach you how to fly and teach you proper techniques in some cases they have "club trainers" and can teach you while you are building yours. Find the experienced builders and pick their brains you can get many good tips and secrets.

Have fun! Welcome to the hobby!