1. Run & Gun page 87 lists common items and modifications that can be added to armor.
For example, both the white noise generator and the jammer is listed as taking up 2 capacity in any armor they're added to. Of course, you could also just carry them around with you.
2. Armor in SR5 doesn't stack unless specifically listed with a + in front of the AV, and even then there may be other requirements.
For example, a helmet can add +2 AV and can be worn with anything, but wearing a set of armored clothes and an armored jacket will only provide the highest AV bonus. The exception to the latter is where Custom Fit (Stacking) is mentioned; for example, a Mortimer of London Berwick suit (Base AV 9) can be worn with an Argentum Coat (Base AV 12, + AV 4) for a total of AV 13. For more information, check SR5 page 169 and R&G page 59.
ETA:
This is more of a rules question than a character creation question, just FYI.