DNM50 26 hours is a long time to spend at the airport.
One very important piece of information is the cabin class(es) of your flights. especially your departure Cabin class. This determines lounge access If it is an F departure then you will have access to Al Safwa. If J then you will have access to Al Mourjan. Both of these lounges have 'rooms' available for resting/sleeping.
The City tour starts from and finishes airside at the airport so you cannot 'pick it up' anywhere else.
Since your transit time is over 24 hours you may have to collect your luggage in DOH and can first check it in again three hours before departure, otherwise you will have no access to it.
Regarding the city tour I would suggest you try for the second or third tour of the day since the first and especially the last are often full.
With regard to leaving the airport and making your own city tour there are a number of posts on this thread with suggestions. Remember that it is Friday and thus a number of small businesses will close to attend Friday Prayers.
By all accounts Doha is a safe city to explore.