Welcome to Tradgang. You want to do a lot of reading here and a lot of searching. Much of what you need to know or want to know has been discussed many, many times.
I'm not saying don't ask, but there is a lot of very good info on here. Do some reading and ask all you want.
Strings are generally 3" - 4" shorter than the bow.
As for the broadheads, 100gr will surely kill a deer, but the issue is total arrow weight and up front weight.
Heavier arrows hit harder. Since you are shooting a bow that is much slower than a compound the same arrow weight will not pack as much of a punch.
Also, more up front weight makes the arrow more stable.
You will need to do some work to find the right combination for your bow. Read the posts on arrow weight, GPP, FOC, etc. Then play around with things and ask questions.
Lot's of helpful folks on here.