Hi with regard to stocking the tank, personally with a 38 gal tank I'd go semi aggressive, 8-10 tiger barbs, a cichlid as the centre piece (maybe a blue acara or a severum) and pictus catfish. Thats what I would do but some may disagree good luck with the tank. In reply to the 50 % water recycling, this will be a waste of time im afraid as it is true, the water holds minimal bacteria so you will need to cycle the tank again. The way to speed up cycling, put some of your existing substrate( if the old setup is still running) into a stocking and place it in your tank. It is packed full of bacteria. If the substrate is dry then the bacteria will have died within 3 days and this excursive is pointless. You can also run your old filter in the tank (if you are changing it) with some of the filter media from your old tank as this is also full of bacteria. Hope to have helped an I hope the switch over goes well
