I am not aware of filesystems on which the bootloader and the kernel could
not be loaded (FUSE filesystems maybe?). Would you tell us more?
However, it could make sense to choose a specific filesystem for /boot. For
instance, is that useful to have a journaled filesystem mounted on /boot? If
Unless you have a justification (I am not saying they do not exist!) for
separating /boot from /, do not separate it. More partitions means a greater
probability to not properly dimension them. You then end up with a full
partition while another partition is almost empty.
No, it won't, if you check "Replace current operating system with Trisquel",
it will install everything either on the HDD or the SSD. You will have to use
manual partitioning.
Select manual partitioning
Create an ext4 partition with mount point / on the SSD
Create a linux-swap
