OK, here is your short short short form of how to change your ROM.
Step 1, find your ROM. First, you go to XDA-Developers and find your device, then you look at the first page or so of the applicable "Android Development" forum at the different active threads. If you have an enormously popular device, you will also want to look at page 2. Look for threads with high post counts. The thread titles should tell you which version of Android the ROM is based on. Check inside the threads to see what is working/nonworking.
Thank you, I see that you really are trying to help. The issue with checking what is working/nonworking is that each thread has on average hundreds of replies, some in the tens of thousands. I _have_ gone and read them, and I still don't know what has been resolved or not. Examples, from the current first page of results:
XDA: DEVDB [ROM] [5.1.1] DarkLord Note 5 Full Port (Fastest, Smoothest) [03/10/2015] 1 2 3
XDA: DEVDB [ROM][AOSP]Minimal OS HLTE Unofficial 2015/10/01 1 2 3
[ROM][5.1.1r18][HLTE] Resurrection Lollipop v5.5.6 [21/09/2015] 1 2 3
[ROM] 03.10.15] [5.0] [Stock] [N9005.../OC3/OEA/OF3/OH3/OI6] QS-N9005-LP 1 2 3
XDA: DEVDB [ROM]AryaMod V7.2 TW Lollipop Official POF3 | OTA Update [14 August 2015] 1 2 3
NOTE 3 SM-N900W8 deathnote v10 snapdragon, Dervish Rom marshmallow 5.0.1
[HLTE/TMO/SPR/VZW][ROM][CM12.1][5.1.1_r16] Temasek's UNOFFICIAL Build v17.3 1 2 3
[Rom][5.0.2][S6 Port][Xposed][18.09.2015] Phronesis Rom v2.0. Stable, Lag Free. 1 2 3
XDA: DEVDB [ROM,TW][03/23/2015] Note 4 port 5.0.1 - DarkLord rom v2.2 N910F BOB4 by Samsungviet 1
[ROm]Note 3 base (tazzy) Aurora-Note3-Full-G9200-Port.v3-Stable,lightening fast. 1 2 3
[ROM] [BOI6] Lollipop And Port Rom [Darklord Note 5 RC Port][10/02]Aurora Note4 Light 1 2 3
[Rom][5.0.2][S6 Port][Xposed][19.09.2015]Norma Rom S6 V15 English 1 2 3
MIUI V7 Note 3 N-9005 v 5.9.25 modded by ENIAC & Atrankas. 1 2 3
XDA: DEVDB [Rom][5.0.1][Note 4 Full port][01.09.2015]AuroraRom Note 4 V6 English 1 2 3
XDA: DEVDB [ROM][OFFICIAL][5.1.1_r18] BlissPop 4.0.3 by Team Bliss [hlte/xx] 1 2 3
[ROM] [hlte] [5.1.1] [official] [CM-based] **crDroid** 1 2 3
[ROM][KERNEL][N9005][OI3][5.0 LOLLIPOP]AUDAX L v29.0[26/09/15] 1 2 3
XDA: DEVDB [ROM][AOSP][5.1.1] Slim ROM Beta 0.7 #Back2Basics [Unofficial][2015-September-21] 1 2 3
Poll: (Xposed) DeathNote Rom Based on Darklord N4 port 1 2 3
XDA: DEVDB [ROM][Official] Tesla by Team Validus [2015/Sep/23] 1 2 3
Choice is good, information is good, but _too_much_ information is just as bad as not enough information. I have seriously tried to go through all those posts but - with no offence to the ROM builders - the ROM builders are busy building ROMs and not documenting their work. We see this all over the open source community: features exist, bugs are filed and fixed, but nothing is documented other than in random, often-contradictory forum and blog posts.
I'm not complaining, I'm just pointing out that the emperor has no clothes: the open source community is does great work, but it is for hobbyists. If I cannot find clear documentation about Foobar ROM, then Foobar ROM is a hobby. I'm looking for something more substantial, and I'll happily pay for it. Maybe Redhat should get into the Android ROM business.