Tequila

You add the 08 (and the 1) first before reversing.
Initially: FFFEB0
Add 08000000: 08FFFEB0
Add 1: 08FFFEB1
Reverse: B1 FE FF 08.
Haven't looked at the rest, but if you followed the instructions it should be ok.

http://feuniverse.us/t/fe7-fe8-display-all-weapon-ranks-your-character-has/744

Basically, start over from the chapter she's recruited in. I assume you'd rather not do that, since you seem to be in the post-game, or close to it. Instead, you can ramhack her rank in using the memory manager. Here's how:
Go to a map where she's deployed.
In VBA, go to Tools -> Memory Viewer
Select her (ie, press A, so you can see the squares to move to)
In the memory viewer, go to 3004E50. The four bytes there are a pointer to her character data in ram. So, for instance, if it says 4C BE 02 02, that should be read at 202BE4C. Go to this address.
According to this, lance rank should be the 0x29th byte. Go to that location and write 0x1F (for D rank).
Check back in the game. She should now have D lances.

It's its own stat. No other stats were harmed in the making of this stat. Lowen probably has PTSD due to repeated time-skipping, but who cares about him anyway?

Yes. Create it in your program of choice, then use this guide to insert it.

EA doesn't like spaces or apostrophes in label names, it seems. Changing Batta's boys to Battas_boys and Two Squires to Two_Squires made it work.
For future reference, put your event file in spoilers, and please use more descriptive labels in your topic other than "Help". We know you need help; that's why you're in the questions subforum. But if someone has a similar question to yours, they probably won't find this topic because the keywords are lousy. Also, there's a stickied topic for EA help.

It sounds to me like you overwrote whatever comes next because the graphic you're adding is larger than the one you're replacing. Try adding it on a fresh rom and leave the "Abort if new graphic is larger than old" checkbox ticked and see if it still inserts. If it doesn't, then insert into free space. D00000-D90000 is confirmed free space. It should either have a bunch of 00's or FF's.

Sure it is. There's a supports module in Nightmare; look at Supports Compatibility Editor, and change the Initial Support Count under the relevant Support Pointer. 81 for C support, 161 for B, and 241 for A.

In FE7, change 40 18 at 292E6 to C0 46.
080292E4 0048 lsl r0,r1,#0x01 @damage is stored in r1. lsl = logical left shift = multiply by 2^1 = 2
08029eE6 1840 add r0,r0,r1 @add the number at r1 (the original damage) to the number at r0 (original damage*2) for a total of (original damage*3).
Zeroing out this second command leaves it at 2x damage. If you want it at something else, like 1.5x or 2.5x, that's gonna be a little more tricky.
In FE8, do the same thing at 2B528.
Does this mean I'm a wise sage now?

1) I'm not sure if I'm understanding this correctly. Are you asking if changes you make using nightmare will affect whatever you've previously done in-game? If so, the answer's no. However, the stuff you change will take effect from that point onwards. For instance, if you play on a vanilla rom until chapter 16, then change Eliwood's growths to all 100, his current stats won't change, but his future level-ups will. Basically, you can't change things that have already been written to the save file.
2) Generally, you want to apply them to a clean ROM to make sure they work. Depending on what you've done to a ROM, it may or may not be possible to patch something; it really depends on what the patch affects. For instance, if you change the location of the item table, and then patch some ASM that uses the item table, the game will break. Most (if not all) patches come with a README.txt. Do exactly as it says: read the thing. It often will tell you what parts of the ROM will be affected. If you're still not sure, patch the patch onto a clean ROM, then use a hex editor to look at the differences between the clean and the patched ROMs. If an area that you've previously messed with is involved with the patch, odds are you'll have to fiddle with it to make it work properly.
Hope this helps!