My suggestion would be to order the LPK, upgraded grip, stock (with buffer tube, etc...) and any other upgrades like KNS pins, etc... in any order you want, but don't assemble any of it until you have all of it. The reason is that there are lower parts that are held in place by the grip and others that are held in place by the stock and buffer tube so if you don't already have these, you can't completely install the lower parts. This means you have to save some small parts that would be easy to lose before the other items arrive.
For a grip, my suggestion is the Magpul MIAD. My second choice would be the Hogue. Both are far superior to the standard grip you will get in your LPK. For a stock, I like the Magpul CTR. However, buy the buffer tube first and make sure you know if you got a commercial tube or a mil spec tube since that will determine which stock you order.