Furniture, Wood and Cabinetry Finishing - staining wood entry door

i just bought a fir entry door, and was wondering what steps should be folllowed when staining it.
1. How many coats?
2. hould the door be sanded between coats?
3. What # sandpaper?
4. Should the last coat be some sort of sealent?
thanks
birch

Wash it with mineral spirits to remove any grease, grime, or fingerprints that it surely accumulated.

Sand with 100 then 150 grit paper. Remove any dust with a tack cloth.

Brush on a coat of polyurethane thinned 50% with mineral spirits and allow to dry over night.

Sand with 220 grit paper between coats to smooth the surface. I would apply at least two more full coats, allowing proper drying time.

I somewhat agree. I would only thin the first coat about 15-20% If you are staining, this must be done prior to the the poly. When sanding always sand with the direction of the grain. Cross sanding will show unsightly once stained/sealed. It usually takes 3 coats of poly to get a good job. The exterior side of the door should be finished with spar [marine] poly. The most common brand is minwax helmsman poly. Each coat of poly serves as a sealant.

what is the purpose of thinning the first coat of poly?
thanks
birch

Thinner poly will absorb more into the wood also goes on a little easier.