I am going to be filing for a trust and SBR my DDmk18 (I know it will take a while).  What do I need to turn the pistol into an SBR?  I assume a buffer tube and stock.  Do I need any special tools to swap it?   Do I need to change the spring or are they the same one?

Nope. Other than paperwork (trust, and form 1), Get a buffer tube and stock. Might as well get the buffer tube kit, that way you will get a new spring, buffer, end plate and castle nut. You may not need them now, but I like having spare parts. Also now is the time to add a sling mount end plate if you think you'll want one. Either a QD type from Say Noveske or Impact Weapons Components, or a loop type like say Magpul RSA or the CQD loop one if you want to stay MK18 correct. All you need is a decent armorers tool or a stock wrench. It doesn't have to be gorilla tight. I usually just go till its snug then put maybe 1/8th to 1/4 of a turn more.

you have to get the lower engraved with the name of your trust too

Usually prudent to get the lower engraved prior to submitting the paperwork,  just to hedge the chance the engraver makes an error in your engraving.

Why waste a lower if the engraver messes up? Legally, it is not an issue if the engraver makes an error. Simply have the correct information re-engraved. Unless it is the serial number (which is not usually engraved because the stock factory SN is usually used), it is not illegal to have multiple model numbers, trust names, cities, states, etc. engraved on a firearm. Aesthetically it may not look nice, but will probablly not detract from the value of the firearm, as most Form 1 firearms do not have much resale value anyway (who wants to buy a firearm with someone elses name engraved on it?).

Do you get it engraved after its been approved?  Or during the time you submit?  

And is efile down?  I am reading that they are coming out with V2 but its not ready yet.

Either way works.

They are down and up regularly. Give it an hour or 24 and you should be able to file.