Hi dread,
1) So... this is one of those difficult questions, which i can't answer, but i have an idea
... those countries, which have common interests with you, form an alliance. but you can't tell a country like russia that it isn't allowed to stay in your alliance...
2) If you declare war on someone, your troops will join your enemy country and fight then... and it makes no sense, when you station your troops in the enemy country and then you declare this country war...
For example: the usa wouldn't station his troops in the iraq und would fight after 2 weeks against iraqi troops. the usa would deploy his troops in turkey like they did...
I suggest you: deploy your troops near the enemy country and increase your troop number in turkey up to 1 million or more.... but this will be difficult, when you have no friends, which help you....
3) So, i do this either for keeping peace in this region and to keep away one country from antoher or to make ready a war against the neighbouring country.
I hope i can help you with my answers...