Any precautions to make before considering renovations?
LL already confirmed can use own contractor and $4000 security deposit refundable after renovation completed. We've so far taken a few photos during our visit and plan to go again soon to take some more. LL insists leaving place in same condition as it is now at the end of tenancy.
Any more actions we should take to ensure there are no problems when handing back the office space in terms of renovations?
This is something to discuss with your contractor, but some things are harder to move than others. Contractors regularly move fire alarms and air conditioning ducts to fit the partitions where you tell them to put them - better to design the rooms to so that they go around such things as the moving costs (and putting back costs) are high. Of course if you have no ceiling high partitions not a problem.