1) Of course solo games are allowed. Many of the examples listed in the main page are solo games.
2) I am sorry I don't understand your question. You can include maps.
3) Frowned upon means they are disliked. If you really have to use emojis, they still fall under 1 symbol = 1 word rule.
4) I am all for using pre-existing cards with words on them (like using a deck of tarot), but if you are making cards for the game, the words on the cards will be counted.