Hey - Welcome along
I think the key bit of advice has been given, buy what interests you and what resinates the best and if you want to dip in slowly stick to smaller sub-lines. Personally i would avoid the exclusives wherever possible, they are really hit and miss and range from easy to find all the way to never going to happen.
When i started collecting modern it was about getting everything (back in the 90's) and then i sort of broke when i realized i just had rooms full of shipping boxes and never actually enjoyed the toys, so had to slim and chose to focus on just the things that really hit home. More recently i have begun grabbing smaller lines again and some of the VC figs but not too much... Honest...
Some of the stuff i have kept does include exclusives. For example i own all the Comic 2-Pack line (a great sub line to collect as it covers all 6 non-disney films and all the old dark horse graphic novels) and two SDCC exclusives and a few Target/Walmart exclusives (there are 66 sets in total i think) so it will take time to get a full house, but not too pricey and the exclusives are easy enough to find.
On the other hand if you go after all the VC figures (180+ since 2010 i think) they you will want to get the SDCC Death Star Revenge set of 12 - that will cost you a kidney and more if you ever find one (I think the last one i saw on evilbay was over a £1000), so not really a realistic goal (unless money is no issue). You would also need the Jar Jar in Carbonite figure and that is a £400/£500 fig on it's own these days. and there are dozens of exclusives on top of that, mostly Target and Walmart 2 and 3 packs, but i would wager it would take years to track them all down now.
While there are exclusives that fit within lines (as above) most don't so as a collection maybe don't sit so well, unless your collection is SDCC or SW Weekends or JediCon or one of the others there have been over the years as they became a way of releasing figures and toys that didn't fit into any other line but fans wanted.
Good places to browse through ranges area to get an idea are:
www.jeditemplearchives.com
&
www.jedibusiness.com
The Black series is nice and i would bet starting with the 40th will lead to other waves being bought (I am sure you know but the 40th has 3 exclusives in it, 2 from Phantom, 1 from Empire) -
For me just look at the line and see if it relates to something within the SW universe you love. If it is or does then grab it, if not - pass.