"Second question : To kill candida I'm planning to do some DMSA rounds... is it possible to start a mercury chelation with DMSA and ALA and taking Iodine at the same time ?"
DMSA tends to exacerbate a candida problem. You might have to limit yourself to using DMSA only monthly or you might prefer to use DMPS along with ALA. You may have to use various supporting supplements for the candida such as zinc and things such as this or similar http://www.wellnessresources.com/products/candida_helper.php
A. Cutler has expressed some concerns about high dose iodine, at least in those who have a heavy metal problem. Mercury messes with the regulation of so many things in the body. Members of the Cutler detox groups don't commonly report use of high dose iodine.
If you indeed have a mercury problem, don't forget to consider the possible involvement of adrenal fatigue. The rule of thumb in some endocrine related groups is to provide some support for adrenals before adding support for thyroid and mitochondria. These can add additional stress to already weak adrenals.