No. It is impossible to have a Telegram account without a phone number, and Telegram uses your phone number as part of its verification process, so you can't enter a bogus phone number, or one that belongs to someone else.
Yes, in many cases. Telegram is capable of detecting many landline phones based on the digits they contain. For others, it is possible to register using the PIN that you'll receive in a voice message.
Compared to landlines, which often use digits unique from the smartphones that Telegram expects, most older ("brick") phones use the same pool of phone numbers. As such, it is almost always possible to register with older (non-smart) phones that can receive text messages. Simply enter your number and use the PIN you receive via text message.
You can set your "last seen" to be private or public. If it is private, users will only see that you are online when you are talking to them. It also enhances other aspects of privacy.
You can create your own Telegram group or join one of many existing public groups. Group chats by default are identical to a direct message, just with multiple participants. You can mute group chats so that you are not notified when a new message is sent, and you can notify a specific person using the @ key followed by their name.
By default, all users in a group chat are capable of changing the group's name or photo. They can also kick other users, as all group members are admins. The group's creator can change this through the Chat Admins settings panel.
A supergroup is a group designed for a large number of people. It is designed for between 201 and 5,000 users, and it provides features that are often key to a large-scaled shared chatroom. For example, new users can view all previous messages. Many public groups are supergroups.
A pinned post is a post in a supergroup that has been highlighted by one of its admins for easy access. Only an admin can pin posts in most groups.
You will need to add the stickers bot on Telegram (@stickers). After that, you must follow the instructions the bot provides you to assemble a sticker pack. Note that the image must be 512x512 or smaller, and one side must be 512. The image must also be a PNG.
You can delete your account via the app's website. You must then use your account to confirm that you intend to delete it. This will permanently erase your non-group messages and contacts.