Regardless from which side you've reached the main area of 4F, there is a relay point right near the stairs. The maze on this floor loops around, so you could start from one side and only explore up to the top center and explore the rest of the map from the other side. Helpful, because at this point your characters won't have many TP.
On the west side of the map are 2 of Alice's dolls, two switches that you'll need to activate for something on 5F, and finally, the mid-boss Ifrit.
On the east side of the map is another doll and the last Peg Insect needed to recruit Wriggle. You definitely want to go back to 2F and "ask" her to join you before you challenge Alice.
Once you've taken out Ifrit, the Chamomile Sigil on the east side of 3F can be passed to get to the fourth and final doll.
At about halfway through, when both paths meet up, you can take a long path all the way to the south. It leads to another one of Aya's notebook scraps.
Aero are probably faster than most of your characters when you first get here. They will hit with a regular attack, a more poweful Swoop, or hit the whole group with Gale. Unless you're underleveled or really unlucky, you shouldn't have any problems.
Mod Golems are very slow, but have high HP and decent defenses. If they do get a turn, hope that they target China, Youmu or Remilia.
Silver Sorceresses can hurt you a lot with their multi-target elemental spells. Always have physical attackers in your active party, as these enemies, like the Bronze Sorceresses, have very low DEF and can be killed quickly that way.
Armour Crabs have decent DEF and high CLD-resistance. Expect Cirno to do little to them.
Wololhands may throw out Strange Mist, which might poison your characters. They do little else and except for MYS-spells, they die quickly from anything.
Single-target physical attack. Expect to be OHKO'd unless Peg Insect targets a wall.
This boss will either OHKO one of your weaker party members, or target Remilia or China who might be able to survive a hit. Regardless, due to its low HP, you should be able to kill it before it causes too much trouble
Another easy battle.. Don't even give it the chance to attack, OHKO and move on towards the other dolls.
Take a moment to laugh in it's face and defeat it. Don't even give it the chance to attack, OHKO and move on towards the other dolls.
Last doll and as weak as the rest!. Don't even give it the chance to attack, OHKO it!
Before you go into this battle, make sure you have only resilient characters in your active party (and especially not Cirno or Minoriko). Ifrit will start out with the multi-target FIR-spell, Flowing Hellfire. After you've taken that massive hit, Ifrit will continue to use weaker attacks for about 3 turns. Your cue is the spell Fireball: If he uses it, he'll follow up with another Flowing Hellfire on the next turn, so switch the more resilient characters back in.
If you've just received a Flowing Hellfire, it is safe to switch in Cirno and Patchouli. With their CLD-spells, no one can beat them in damage against Ifrit. If you're always ready for Flowing Hellfire, this battle is very easy. Get used to this procedure, some bosses you will encounter later work similiar to this one.
Alice and her group of dolls is a battle which is nearly impossible if you go in without a strategy, but fairly simple if you know what you're doing.
Beautiful Light and Magical Light attack you with fairly strong physical and magic attacks respectively,
while Alice uses single target Silence or Paralysis spells.
The main problem is Healing Light, which will restore roughly 10,000 health to any one enemy that gets low or 700 health to all enemies at once. It can also debuff a character, having a chance to lower all of their stats.
It won't cast the single-target heal on itself, but Magical Light and Beautiful Light will immediately boost the defenses of Healing Light up to +100%, which prevents most attacks from damaging it.
The ideal way of getting around this is by destroying it quickly using defense-piercing spells, namely Patchouli's Silent Selene.
Once Healing Light is defeated, Magical Light and Beautiful Light can be focused down easily, leaving just Alice.
As her dolls are defeated, Alice switches from using all status attacks to attacking you directly, but she's nothing particularly difficult to deal with. Alice is somewhat resistant to all elements, so non-elemental attacks work better on her.
It's worth noting that Magical Light is vulnerable to Cirno's Speed loss debuffs and Beautiful Light can be affected by paralysis, while Alice herself is vulnerable to both.
It's also worth noting that all four are vulnerable to Wriggle's poison.
Another strategy is to boost your party with Lunar Clock and destroy either Magical Light or Beautiful Light in between heals with the strongest spells you have, but this tends to require a higher level than aiming for Healing Light.