ppg primer/sealer

I am using concept urethane for my top coat but am unclear about sealers and primers. On the bare metal I was going to seal with dp40lf. Then spray k36 primer surfacer as many time as needed, reseal with the dp and then color. On the body (fiberglass) I was going to start with k36 ,again as much as needed, seal with dp then color. I have two questions:

1. The k36 product sheet states that it can be used as a sealer as well as a primer surfacer depending on the additives used, so is it necessary to use the dp sealer or should I use the k36 for everything and mix accordingly?

2. Should I clear coat. It's a solid color, no metalic. I will be color sanding as I want a glass smooth finish. I also noticed the product sheet for the concept gives the option of adding the clear in the last coat. Which, option if any, would be better?

With the price of paint I don't want to buy something I don't need but at the same time don't mind paying for it if it's needed. Thanks.

1) DP then k36 then DP again

2) Clear over the color, no need to add color to clear

OK that's what I've done in the past but wasn't sure if could get by with using only one type of surfacer/sealer instead of the two like I have been doing, thought it might be cheaper for one.

Also is it necessary to clear coat? What are the advantages or disadvantages to clearing? Like I said before, I'm going to color sand. Will the finish be better color sanding and buffing clear or no clear and color sanding and buffing?

1) The DP will act as a primer and to some degree as a sealer. More of a primer when used over metal and more of a sealer used over primer/surfacer. I would consider using a sealer after the second application of DP and prior to basecoat. Sealers are optional and will gaurantee no bleed through and more color consistency. If you want I can suggest one after I look it up.
2) Clear coat is also an option.It really depends on the affect you are trying to achieve. If you are looking for a deep gloss wet look then clear coat it. Apply it wet and don't worry too much about runs, they will wet sand out. I usually apply the last coat of clear with an extra ten percent of reducer for better flowout. If you do not clear, PPG DCC single stage works well and give you an excellent finish. Good Luck!