1: What are the core shops ? the ones that are worth giving your money too and supporting your local ?
By no means a complete list but Slam City Skates and Parlour are the ones that spring to mind in London.
Online would be SS20, Native, Endemic, Bored of Southsea and Reskue.
2: What brands are most popular ? Can I pretty much get anything or is it more UK / Euro brands ?
Palace has taken over boardwise in London but still a decent plurality of brands.
3: Cheapest places to live in London ? best way to get around in London ? buses or subway ?
Cheapest in central is generally the roughest. Elephant & Castle, Peckham, Brixton are cheapest in central but if you don't mind travelling then head out to train zones 4/5/6. Best way to get about varies heavily depending to time of day, weather etc but the tube seems to be the best.
4: What time does public transportation close down at night ? buses and subway ?
I live in Zone 6 so I don't have a clue about tube times but trains stop at about 12:30am but then night buses operate.
5:Any spot guide or any spots I need to check out ? I mostly skate ledges and manual stuff . How are police against you ? Illegal to skate or pretty legal ? people harassing you ?
Spot wise, a lot of places are a bust but only after 10 minutes. Elephant & Castle manual pad and blocks are hassle free and St Pauls area is usually okay.
North of the river i.e. St Pauls area is City of London police force who are generally decent guys that don't care but have to tell you to not come back. They usually say skating is illegal under an 1800's bylaw concerning four wheeled vehicles without brakes but its more idle threat than precedent.
Everywhere else is Metropolitan police territory who are the same in that they don't care but have to move you on.
6: How is the community ? people friendly ? any skate bars ?
Skater wise, people are usually in groups. A bit of interaction but generally stick to who they know. No skate bars.
7: Any Slap pals in London who wanna skate or get drunk ? Slap pal meet ups ?
I don't drink ha
8: Any outdoor / Indoor parks ? Mini ramps ?
Mile end, Stockwell, Walthamstow, Southbank, White Grounds, Bay 66, Meanwhile 1 & 2, Victoria, Harrow, Dagenham, Kingston + More
Hope that helps