You should tell us about any health issues early in the assessment process so that we can consult a medical professional and advise you appropriately. All adopters undergo a medical assessment.
Passive smoking is now recognised as being harmful to adults and children so if you want to adopt you should be a non-smoker or to have stopped smoking for a period of one year if you want to adopt children 0-5 years old. All prospective adopters will be expected to maintain a smoke free home.
Being a bit overweight will not stop you adopting a child, it only becomes a problem if it affects your health or ability to care for a child.
If you are disabled, this in itself is not a barrier to becoming an adoptive parent. It is your ability to parent a child that is important. However if your condition has implications for your life expectancy, or involves symptoms which may take looking after children problematic, then this would need careful consideration.