A perennial subject Anthony but one which one often brings out new ideas. You can search the reflector archives to see what was said before.
I used 7/0.1 stranded PVC hookup wire, light, never snapped in GM weather in 350 activations. Yellow stands out well. RG174 will do fine for the feeder.
For SSB 40/20/17/10. You should be able to use the 40m dipole on 15m. You may want to consider 60m.
There’s a thread about my balun! Do I need a balun? - #10 by GW7AAV 
Check out http://www.sotamaps.org/extras.php for a linked dipole calculator to make things easy.