Yes sounds like you are a poor excretor of mercury (sorry it sounds like an insult!). Very low mercury hair levels can indicate poor excretion, but also depends on the levels of your nutrient minerals.
Yes other metals will come out before mercury gets excreted. It does sound like you are dumping them and potassium too, or at least your cells aren't able to hold on to the potassium. Adrenal support may help.
DMSA chelates lead and mercury. ALA chelates arsenic and mercury. For the other metals it will be a case of sorting out the mercury, correcting any mineral imbalances, and maybe avoid contact with certain materials eg antimony is in flame retardants.
In another post of yours you said things are going well. I would stick to what you are doing.
In the meantime I would suggest getting Andy's hair test book which will help with interpreting your hair results more accurately and/or post your hair tests here or on the autism mercury group for more advice.