For sustanon estrogenic side effects are dose dependent. i assume you will not be using theraputic doses when sides wouldnt be too much of an issue. According to Anabolics 9 th edition(try to get this book it has all the answers re AAS and more besides) you can use clomiphene citrate or tamoxifen .You can also use an AI instead, but can have an effect on blood lipids.Elevated estrogen can lead to water retention, body fat gain
as for deca estrogen conversion is lower than test, however nandrolone is a progestin and the side effects are similar to estrogen, so a combination of the two could contribute to side effects such as gyno, so an anti estrogen is recommended. source; ANABOLICS 9TH EDITION BY WILLIAM LLEWELLYN