Which Platform & Which Membership Software?

Hi chaps - best to assume I have zero knowledge here. I'm teaching myself as I go along but I'm no natural and am beginning to get a bit bogged down. I am trying to do things on the cheap (or, rather, avoiding being ripped off), so would like to set things up myself wherever possible.

I currently run the sports tipping website gttips.co.uk/home [unable to link] but am looking to rebuild. What I want to install is a fully functioning Membership software, and get away from the clumsy single password protected blog I have at the moment.

I have been scanning these forums and found a few threads that have helped me a lot - but some are old, and I would appreciate if anyone has any specific suggestions for someone in my situation.

Firstly; is Wordpress the best platform for me to build a new site, given that the main new functionality I want to install is Membership software? My site has a very simple structure of a few blogs, one for each sport, and I'd like to create a password protected members only blog / area (or maybe make individual posts members only, with teasers etc).

Secondly; are there any web-based / html / css based membership software programs that I can integrate into tumblr?

Thirdly; if I do build a site in Wordpress, do I need a .com or .org site to install these membership software plugins? I currently own the gttips.co.uk domain (but can't remember which provider it's with - can ask the guy who set it up for me) - if I set up a WP owned domain, will there be issues when I switch gttips.co.uk to direct at the wordpress content instead of the current tumblr content?

Fourthly; Should I set up my Wordpress blog first, or get the Membership software up and running before designing my blog?

Fifthly; which Membership Software is best for my needs? Here's my best guess at what I need/want/don't need...

I need software that will allow different Membership periods, ie 30/90/365 days and will automatically block access to a user when their time is up.

I need software that has an 'auto-renew' option.

I need the software to link with paypal.

I would like the software to link with mailchimp, but could move to AWeber if necessary (or recommended).

I would like the software to have different access levels (gold/silver etc)

I don't need drip content, as my old content is defunct/outdated.

S2Member, Wishlish Member, WP Memberchamp, DAP and Member Guardian have all been recommended in various places - does anyone have any views about which would suit me best? Do any of them have hidden costs beyond the initial fee? Is there anything I've missed that I should be taking notice of?

Thanks in advance - if anyone helps and fancies a GT Tips membership just give me a shout and I'll get you added free of charge

~GTT