Understanding linker script values in the context of a simple kernel

Question

I'm following this book with regards to developing a little kernel: https://littleosbook.github.io

I've gotten to the point where the binary has to be linked and I want to be sure that I understand the linker script before proceeding:

ENTRY(loader)                /* the name of the entry label */
SECTIONS {
    . = 0x00100000;          /* the code should be loaded at 1 MB */
    .text ALIGN (0x1000) :   /* align at 4 KB */
    {
        *(.text)             /* all text sections from all files */
    }
    .rodata ALIGN (0x1000) : /* align at 4 KB */
    {
        *(.rodata*)          /* all read-only data sections from all files */
    }
    .data ALIGN (0x1000) :   /* align at 4 KB */
    {
        *(.data)             /* all data sections from all files */
    }
    .bss ALIGN (0x1000) :    /* align at 4 KB */
    {
        *(COMMON)            /* all COMMON sections from all files */
        *(.bss)              /* all bss sections from all files */
    }
}

First of all, why the specific ALIGNment of the sections (4KB)? (I think it's very unlikely to be related with optimizations or I could me mistaken and this may be for performance reasons, since otherwise I think there's no restriction on the boot process - confirmed by removing the ALIGN function calls in the script)

Then considering the executable to be linked:

 global loader                   ; the entry symbol for ELF

    MAGIC_NUMBER equ 0x1BADB002     ; define the magic number constant
    FLAGS        equ 0x0            ; multiboot flags
    CHECKSUM     equ -MAGIC_NUMBER  ; calculate the checksum
                                    ; (magic number + checksum + flags should equal 0)

    section .text:                  ; start of the text (code) section
    align 4                         ; the code must be 4 byte aligned
        dd MAGIC_NUMBER             ; write the magic number to the machine code,
        dd FLAGS                    ; the flags,
        dd CHECKSUM                 ; and the checksum

    loader:                         ; the loader label (defined as entry point in linker script)
        mov eax, 0xCAFEBABE         ; place the number 0xCAFEBABE in the register eax
    .loop:
        jmp .loop                   ; loop forever

Am I right when saying that the .rodata, and .bss sections are not yet needed? (since the kernel still starts fine)

Is there anything else to understand form this little linker script that I cannot get out of the the ld manual (which I read a bit to understand the dot, the SECTIONS and the entry point)?

It seems that I can re arrange the sections' order in the script and the kernel still works, why is that?