-The foregrip is pointless as the 98 custom already has one and does not have the rails to attach that one. -The flatline barrel is a worthwhile upgrade. You should do some research into an apex barrel as it can be equally awesome. -RAP4 vests have always been good from what I've seen. You shouldn't have any real problems with this. A good price as compared to a molle vest with attachments. -I would strongly recommend against that particular remote line, I had one and it had lots of problems. An excellent choice would be the Guerilla Air Cobra, I've found this to be far superior to any other remote line I've seen. -Collapsable buttstock is fine. I personally prefer a folding stock but lots of people prefer collapsables. -98c, good, reliable starter marker for someone who is solely playing woodsball/scenario.
My own suggestions:
-As an alternative to a 98c with stock and foregrip you could save some money by getting an Azodin ATS+ which costs around $120 and comes with collapsable stock and foregrip. -I reccomended this to a friend of mine a while back, he had similar desires to you and he's loved it and hasn't had any problems with it. -The only problem with doing that would be that you would not be able to use a flatline barrel. However you would still be able to us an apex barrel. If you have any questions about apex vs flatline I'm sure the forum here would be happy to help. -Any money you have left should go towards a good quality mask first, THEN a half decent hopper (You don't need any overexpensive loaders for woodsball) ,THEN a basic HPA tank.