I would agree with LB on this. The cost difference between 4 more vs. 8 more Gigs is not enough to deliberate on.
Plus you may have to pay almost twice if you do it in 2 stages.
For example:
Currently you have 8 gigs. If you pay for 4 sticks of 1 Gig each, it might cost you $60-80.00.
That’ll give you 12 Gigs.
Then if you later decide you can & will go with 4 sticks of 2 Gigs each to bump up to a total of 16 Gigs for say $100-120, that first $60-80 will now be wasted.
And although you could sell those first 4 - 1 Gig sticks, RAM is so affordable these days, you’ll get very little for them.
I’m sure if you ask 100 people about this, the 85 that are worth listening to will tell you that the 70 who actually know something about this will say just go for the 8 more Gigs [16 Gigs total] in one go, giving you more RAM and more savings in your pocket, not to mention the small hassle of doing it just once vs. twice!