you can only separate two things with a semicolon when you use the bind command, you'll need to make aliases and bind those to 1/2/3

also you can't nest quotations, "cl_crosshair_file "crosshair7"" doesn't work

Thanks.

for reference you can't separate more than 2 things with a semicolon in general, so you'd want to make an alias with two commands, then bind the key to the other command you need and the alias

since you've got viewmodel_fov 90 for everything you don't need to redefine it with ever binding, just set that in your autoexec, and then you can do something like

alias gun "r_drawviewmodel 0;cl_crosshair_file crosshair7"
alias melee "r_drawviewmodel 1;cl_crosshair_file crosshair5"
bind 1 "gun;slot1"
bind 2 "gun;slot2"
bind 3 "melee;slot3"

this is off the top of my head, so if it doesn't work I apologize, but there's a handy page on the tf2 wiki about ingame scripting here

You can definitely separate more than 2 things... you just keep adding semicolons. The only issue OP had was with the nested quotes.

bind 3 "slot3; r_drawviewmodel 1; viewmodel_fov 90; cl_crosshair_file crosshair7"
bind 1 "slot1; r_drawviewmodel 0; viewmodel_fov 90; cl_crosshair_file crosshair7"
bind 2 "slot2; r_drawviewmodel 0; viewmodel_fov 90; cl_crosshair_file crosshair5"

Should work.

Here's a much more in-depth page about scripting in TF2 to help you learn.