It comes down to personal preference, there are pros and cons to sending them all or just a few at a time. By sending them all at once you are spreading the fixed costs of shipping (both ways) and handling fees over a larger number of coins which reduces the per coin cost of submission. However there is greater risk of loss if your one package is lost or stolen in transit, the old having all your eggs in one basket. Not trying to worry or scare you but every now and then packages have gone missing so while the chances are minimal it is a real risk. Its really up to you to decide which way is better and more comfortable for you. One tip is that if your sending them all be sure you only send by registered mail (assuming your sending via the USPS), it is the safest and most secure method the USPS offers. Honestly registered is the only way I ship as it lessens the risks, takes longer than priority but I feel better with the added safety. As you have sent in one group I would wait and see how these grade, in other words use these as a test to see how your expected grades compare to the grades NGC assigns. You can then decide if your ready to go all in or reevaluate the idea.
At any rate best of luck with your current submission as well as any future submissions.