Nolvadex will clearly inhibit your gains due to it's impact on IGF-1 levels. Especially, since it is a Test only cycle. 20 mgs ED should be fairly effective without having too much of an impact on your gains.
How have your previous experiences been?
I would strongly recomend going with an aromatase inhibitor such as Aromasin, Femara or Arimidex. Prevent the side effects before they even start. Also, they don't have the negative impact on your gains such as Nolvadex. Aromasin would be the best choice due to it's overall effectiveness and minimal if any impact on your cholesterol levels.
My friend is currently running 750 mgs Sustanon along with 1 mg Arimidex EOD. He started with .5 mg EOD. No gynecomastia but there was still some water retention. He bumped up the dosage to 1 mg EOD and that minimized everything.
Also, 1 mg Finasteride ED isn't a bad idea either to minimize hair loss and to keep the prostate healthy.