Yes, you have to be a member to get a moshling on Moshi Monsters. However, there are two kinds of members; a free Basic Membership or a paid Moshi Membership.
There is a Basic Membership for Moshi Monsters which is free, but you will not be able to do all the activities or catch all the Moshlings. With a Basic Membership, you can get all of the moshlings except the ones that need a Snap Apple, a Crazy Daisy, or that are part of a Super Moshi Mission, or that need a Limited Edition Code for a specific seed. You can keep 2 moshlings in your house and keep one moshling in your backyard.
There is a Moshi Member (paid membership) where you may have up to 6 moshlings in your room which can be swapped any time and the rest are kept in your Moshling Zoo. You can access all areas of the site including Moshi Island, Gift Island and the Port and you receive a VIP pass to the underground disco. Moshi members get rare and exclusive moshlings and can become Super Moshis by completing Super Moshi Missions.
Yes, you must be a member to take your moshling for a walk on Moshi Monsters.
You can not become a moshling on Moshi Monsters. You can attract moshlings to your Moshling Garden and collect them in your Moshling Zoo (if you are a paid Moshi Member).
You have to be a paid Moshi Member to have access to the Moshling Zoo through the Moshling Zoo Door on Moshi Monsters.
You have to be either a free Basic Member or a paid Moshi Member of Moshi Monsters to get the moshling Dipsy.
You have to be a member to have your moshling follow you.
No, you do not have to be a (paid) member on Moshi Monsters to get Peppy the Stunt penguin.
If you are a member on Moshi Monsters, the latest moshling you have captured will be following you. I'm not sure why though!
There is no moshling on Moshi Monsters named Big Ben.
You can get Chop Chop on Moshi Monsters if you are a free Basic Member or a paid Moshi Member.
You can not take your Moshling for a walk unless you are a Moshi Member (paid).
You have to be a moshi member!
You can not delete moshlings on Moshi Monsters. If you are a free Basic Member, you can choose "Set It Free" when you get a new moshling, but the moshling that you set free goes to your Moshling Zoo in case you ever get a paid Moshi Monsters account. If you are a paid Moshi Member, moshlings go to your Moshling Zoo.