Mature gamers will find that Illyriad supports a deep game that tests many of the rationalist virtues.
Is there anything I should bear in mind when creating an account?
It is possible to start the game with an advantage if you are recommended by an existing player through the buddy program. This earns the recommending player 100 prestige upon getting to the population required for a second town, which will indebt that player to you. It is reasonable to ask for a prestige scrap or 20 million in gold in exchange. Alternatively that player can help you grow and owe you a favour. If you would like to take me up on this offer, sign up using the link http://illyriad.com/?347401 - other players might advertise their conditions at the Attracting new players via the buddy program thread I created at the Illyriad forum: possibly their terms are better than mine.
The best choices for races at the start are probably elf (which has the edge for war, see Warmongering In Illyriad: The Best Race for N00bs) or orc (which is probably the best choice for trader/gatherer); gender doesn't matter.
Should I join an alliance?
The main practical consequences of joining an alliance are that the social circle who you are involved on includes the people on your alliance's chat. If you are in an alliance, that means that these are the people you should beg for resources, while if you are not in an alliance, begging on general chat, while officially not allowed, will tend to get you lots of free resources. How much and how fast you get resources when you are in an alliance depends on who the other players are: if you join an alliance of small players or one that is not so active, you will be hampered growing at the start.
Asking about which alliances are recruiting on general chat is probably a good idea; you are likely to get pointed to one of the forum posts about choosing alliances, but chatting is a better way to figure out which alliances are the best fit for what you want to get out of the game. Don't be afraid to join and leave several alliances until you find one that is a good fit, and don't move your towns to an alliances hub before you feel committed to them.
Some players prefer to be independent, although in my view it is mostly missing out on the best of what the game has to offer.