I've installed picofly and followed retry guide but something is not yet clear.

Have you tried powering on without the SD, getting the no SD card pico screen, shutting it down and turning it pack on with both volume buttons simultaneously? XCI is a cartridge dump, while NSP are packed digital content. What do you mean show like tinfoil?

Why on Mariko I don't have the possibility to boot on OFW? It seems that rentry guide add the code for stock nand only for Erista.

You can, just replace your ini. Open your hekate_ipl.ini file with Notepad. (it's inside the bootloader folder on your SD)

Delete everything inside the ini and paste the following in:

[config]
autoboot=0
autoboot_list=0
bootwait=3
autohosoff=0
autonogc=0
updater2p=1
backlight=100

[Atmosphere FSS0 emuMMC]
fss0=atmosphere/package3
kip1patch=nosigchk
emummcforce=1
icon=bootloader/res/emu_boot.bmp

[Atmosphere FSS0 sysMMC]
fss0=atmosphere/package3
emummc_force_disable=1
icon=bootloader/res/sys_cfw_boot.bmp

[Stock sysMMC]
fss0=atmosphere/package3
emummc_force_disable=1
stock=1
icon=bootloader/res/stock_boot.bmp

Can I update emuNand (file) to lastest fw? I'm on 15.0.0 now

Yes. You can update the emummc with Daybreak. Boot into OFW (Stock), and update it to latest.

Then follow this guide to dump your FW from stock and install it on emu: https://nh-server.github.io/switch-guide/extras/updating/#updating-emummc-by-dumping-an-updated-firmware-from-your-sysmmc

I see different file type for game like xci and nsp what is the difference? Should I have to use app like goldleaf?

DBI can install all Switch game files (NSP, NSZ, XCI, XCZ). See this guide for installing them: https://rentry.org/NSUSBInstall/#dbi-installer-mtp