Yes you can but it is not an exact science, there is likely to be an element of trial and error. Many beams and shelfs can help to divert the heat. This is to deflect the direct heat from your appliance. For many years, people have placed art above fireplaces without issue.
However, this depends on how often you use your fireplace. Be wary and vigilant and be prepared to take temperature readings so that it does not exceed manufacturers recommendations. Please do not take this as advice to place objects above fireplaces.
A smoke tested and commissioned HETAS passed stove will not affect your house insurance, we recommend contacting your insurance supplier none the less.
Wet wood and treated wood will damage the flue liner of your chimney. Stoves are typically multi-fuel or wood only, depending on the stove. Wood is the best considering it is carbon neutral but anthracites can also be used but please do check the manual for the necessary fuels.
The most common reason for blackened glass is damp or wet wood. Anything over 20% moisture content is classed as wet and should not be used. Not only will you get blackened glass but you will also not benefit from the full heat output of your stove due to the moisture cooling the flue gasses. This will also damage your flue. Burning damp wood for a long period of time can tar up the flue, block the flue and in worst case cause a chimney fire.
There are many different sized cages and barriers that would be perfect for youngsters. Please advice your children on the dangers of touching a warm stove to refrain them from touching it. The choice is ultimately yours and assessing the risk of your setup and little ones.