The first application of stains do 90% of the coloring. A second application will slightly enhance the color but there won't be much penetration since the first application already did that. If you want a darker or different color than what is available, you can mix two or more colors before applying. Applying more than two coats on won't work that well and the extra applications may lift since they can't penetrate into the wood. All applications should be wiped off completely, you don't want to leave a film of stain on the work. Minwax does have a sealer in it, on the can, it's called "wood finish" although it doesn't offer much in the way of protection. It just makes additional coats less likely to do anything. This is even more the case when you have used a conditioner since that is also a sealer.