Quote by @krd0429 on 1 hour ago

......making a 3 layer cake, using two boxes of DC french vanilla cake mix. My plan is to:

Replace water with milk, equal proprotions

Answer:  that's fine.  Many people do that:)

Add an extra egg per box mix 

Answer: I see no reason to add an extra egg but if you really want to I have heard on here of others who do.

add a teaspoon of vanilla extract

Answer:  That will boost up the favor a bit:)

Replace the oik with butter (how much butter should i use? 

Answer:  Again, oil (or butter) is not necessary.  I have made 100s of cakes w/o any.  Some people think itboosts the flavor.

A box of pudding. I was originally going to use 1 box per box of cake mix, but then I thought it would be too much, so i decided on using only one box of pudding for both of the mixes.

Answer: Adding pudding mix adds more sugar to the recipe.  It is totally unnecessary in my Opinion.  Yes, there are others who have said on here that they do.

Will this come out ok?? 

Also, for stabalizing whipped cream I am stuck between adding pudding, or adding unflavored gelatin. What have you used and what method, and which do you prefer? 

Answer:  Never hve made stabalized whipped cream.

...1 more question! ...... two boxes and spread... out into 3 9-in rounds, will 1/2 gallon of heavy cream whipped be enough to fill and frost the cake? 

Though as I said, I have never used it I would guess that it will be more than enough.  If you want to use it all on the cake just 'ice' it thicker:)