Here you go ...
 

1. At last! A rustic thinks a queen among elves as fair as one of these.
2. A third of this is what we need – due to answer number five? Or at Bombadil’s - for cut knees, perhaps?
3. Streaming things for which this housekeeper holds the key? That’s a first!
4. Wait a second. This is why you might need an understudy in a Shakespearean tragedy. Confused, and flowery.
5. Horse with highlights is confused in shining Sindarin. Take nought from the third?
6. It’s both long and longed for – by a dwarf. Go fourth.

#1 and #6 are giving me Galadriel vibes. #1 sounds like Sam's speech to Faramir (but which of the similes?), and #6 sounds like the lock she gives to Gimli (but again, by what synonym? Lock? Hair? Strand? Tress?).

1. At last! A rustic thinks a queen among elves as fair as one of these.
2. A third of this is what we need – due to answer number five? Or at Bombadil’s - for cut knees, perhaps?
3. Streaming things for which this housekeeper holds the key? That’s a first!
4. Wait a second. This is why you might need an understudy in a Shakespearean tragedy. Confused, and flowery.
5. Horse with highlights is confused in shining Sindarin. Take nought from the third?
NERWEN'S HAIR: It’s both long and longed for – by a dwarf. Go fourth.

Any will do fine for 6.

For 1, the answer is indeed in one of the similes.

Hints?

OK!

Number 3 has a very similar answer to Number 5.

and

Galadriel was very close to solving clue 1, (upthread).

For #1, we're looking at this quote:

Since the clue is "fair as", I would guess either GREAT TREE or DAFFADOWNDILLY... um, DAFFODIL for the answer.

hS

DAFFADOWNDILLY: At last! A rustic thinks a queen among elves as fair as one of these.
2. A third of this is what we need – due to answer number five? Or at Bombadil’s - for cut knees, perhaps?
3. Streaming things for which this housekeeper holds the key? That’s a first!
4. Wait a second. This is why you might need an understudy in a Shakespearean tragedy. Confused, and flowery.
5. Horse with highlights is confused in shining Sindarin. Take nought from the third?
NERWEN'S HAIR: It’s both long and longed for – by a dwarf. Go fourth.

Hence the 'At last.' ;)

I solved a clue
I solved a clue for you
Oh what a thing to do!
And is the code YELLOW?

hS

DAFFADOWNDILLY: At last! A rustic thinks a queen among elves as fair as one of these.
????E???? A third of this is what we need – due to answer number five? Or at Bombadil’s - for cut knees, perhaps?
L?????? Streaming things for which this housekeeper holds the key? That’s a first!
????L????Wait a second. This is why you might need an understudy in a Shakespearean tragedy. Confused, and flowery.
????O???? Horse with highlights is confused in shining Sindarin. Take nought from the third?
NERWEN'S HAIR: It’s both long and longed for – by a dwarf. Go fourth.

Indeedydo.

Okay, so: 3 and 5 are very similar. I think 3 might be another 'Someone's Something'. That means 5 is either the same person or the same thing. Additionally, 2 references 'answer number 5', which likely means the, uh, actual answer to question 5. So solving any of these three will help with the other two.

The letters we will need are 3rd - 1st - 2nd - probably 3rd.

If the Bombadil reference is direct, then things called yellow at Tom and Goldberry's are:

- Her hair
- His boots
- Cream
- The sunrise

CREAM seems to fit best, though I don't think the sort of cream Tom serves would go well on your knees!

hS

DAFFADOWNDILLY: At last! A rustic thinks a queen among elves as fair as one of these.
CREAM: A third of this is what we need – due to answer number five? Or at Bombadil’s - for cut knees, perhaps?
L?????? Streaming things for which this housekeeper holds the key? That’s a first!
????L????Wait a second. This is why you might need an understudy in a Shakespearean tragedy. Confused, and flowery.
????O???? Horse with highlights is confused in shining Sindarin. Take nought from the third?
NERWEN'S HAIR: It’s both long and longed for – by a dwarf. Go fourth.

Yes. Bombabil particularly refers to yellow cream, amongst other foodstuffs.

You are right about the positions of the 'red' letters, too.

I am gonna throw out LOCKS and ELANOR for the first two of the remaining clues. Locks, because it sounds like it should be hair. And Elanor because the letter fits.

It's LOCKS OF someone, but which blondie do we see being a pretty much full time housekeeper?

(Also, locks have keys, and so do housekeepers).

DAFFADOWNDILLY: At last! A rustic thinks a queen among elves as fair as one of these.
CREAM: A third of this is what we need – due to answer number five? Or at Bombadil’s - for cut knees, perhaps?
L: Streaming things for which this housekeeper holds the key? That’s a first!
ELANOR: Wait a second. This is why you might need an understudy in a Shakespearean tragedy. Confused, and flowery.
????O???? Horse with highlights is confused in shining Sindarin. Take nought from the third?
NERWEN'S HAIR: It’s both long and longed for – by a dwarf. Go fourth.

Oh, sorry! You were guessing ELANOR for the 4th clue.

Quiet rightly. Because you would need an understudy if there were NO LEAR in the building.

Number 3 is LOCKS OF someone, but please say who, (see my post upthread).

LOCKS OF GOLDBERRY? I think I remember enumerating her as something yellow when I was figuring out cream.

On no more basis that this and 5 are "very similar", I'm going to guess BOOTS OF BOMBADIL for 5.

hS

DAFFADOWNDILLY: At last! A rustic thinks a queen among elves as fair as one of these.
CREAM: A third of this is what we need – due to answer number five? Or at Bombadil’s - for cut knees, perhaps?
LOCKS OF GOLDBERRY: Streaming things for which this housekeeper holds the key? That’s a first!
ELANOR: Wait a second. This is why you might need an understudy in a Shakespearean tragedy. Confused, and flowery.
????O???? Horse with highlights is confused in shining Sindarin. Take nought from the third?
NERWEN'S HAIR: It’s both long and longed for – by a dwarf. Go fourth.

Sorry; it's 3 and 6 that are very similar, (as you can see).

Tom's boots are wrong, I'm afraid.