To get professional-looking splices in wiring without electrical tape, try head-shrinkable tubing. Slip a tube on one of the wires before splicing. After splicing, move it over the splice and apply heat with a heat gun. The tubing will shrink down for a neat, protective covering. You can buy tubes in multiple sizes, as well as shrinkable wire caps to use in place of screw-on wire nuts. They're perfect for work on vehicles, trailers, underground and pool wiring, or for outdoor lighting or sprinkler systems.
When planing a major renovation project you will increase your chances for a successful outcome if you hire a contractor with whom you feel comfortable. Make sure the contractor has experience in renovation. Always check references and make every attempt to see current and/or previous work.