I use the same SS 5 gallon kettle I started with for PB/PM BIAB. I do 5-6lbs of grains in 2 gallons of water in a large nylon bag with a cake cooling rack in the bottom to keep the bag of grains from burning on the bottom of the kettle. Use the 2G to heat 1.5 gallons of sparge water (what I do) while the 1 hour mash is going. After the mash,I use a polished SS collander I got at Bed,Bath & Beyond for $9 on top of the kettle to place the now draining bag of grains on. Then sanitize a 2C pyrex measure to slowly pour the sparge water evenly over the grains in the bag in the collander on top of the BK/MT.
Allow to drain well,then proceed to the boil.
**By the way,this gives 3.5 gallons of wort for your boil volume. Depending on how much grains/extract I use,I get 5 or 6 gallon batches with ice cold top off after chilling the wort down to 75F or so,before topping off to recipe volume in the fermenter.