Paint the tube interior flat black. Or make up your own, creative technique for painting the interior. Predrill all screw holes to prevent cracking. Use screws for attaching wood to wood. Test your telescope thoroughly for a few months before gluing.
Most people find that gluing the wooden pieces together is unnecessary.
Use wood filler to fill any cracks or chips, then sand the patches smooth. Water-based polyurethane products varnish will allow you to work fast and produce a beautiful finish on wood surfaces. Sand and stain first, of course. Put a dot on your primary mirror. Place the mirror face down on a sheet of paper and trace around it.