Hmm, I am not sure why you would need to tear it down and start again. The tank can be brought back from the abyss so to say and should take all that much to do it. The pleco is way too big and needs to go. A good show tank in a really good LFS would be a nice place for him. The other fish might be ok but that depends on what you want to do with the tank.
I would do a really good gravel vac with about 1/4 of the water and refill the tank I would say 1/2 water change but fish are too big for that. If you can, do 1/4 water changes 3 times for a week. This will clean the gravel really well and should have a good base to start over. As for the glass, if you plan to get rid of the larger fish, got some ottos, 6-10 of them would have a picnic for days and be very happy campers. With every water change, rinse the filter media really, REALLY well in the tank water to get it as clean as possible. Also, take the filter and scrub it clean after a week in tank water to get the all the gunk out. This will keep some of the bacteria in place and not hurt your biological filtration needs.
It is really up to you but a I have seen tanks come from green pea soup where you couldn't even see into the tank through the glass because it had tons of algae on the glass and green water to pristine tanks in less than a month.
It will help to tell us the type of filter so we can help with the media and cleaning it.
As for the biological bacteria in the filter, if you tear the tank down you will need to keep the filter running in a smaller tank or a bucket of water to keep the bacteria alive or it will die in a matter of a couple days. Also will need to feed the bucket or tank so the bacteria has something to eat to survive.
If you need help getting it all done ask as many questions as you need to. Could be a great article for the forum, Rescued a tank from algae oblivion. 8)