Help needed asap

Hi there everyone my names conor and I've just joined the forum after asking around and getting useless answers from bike stores iv decided I should speak with proper cyclists .

I have been using a specilized tricross for around 2 years and loved it but decided to get a new mountain bike to do a bit of river paths and rougher terrain

So I brought a carrera hellcat 29er and for the price I got it at (£185 + kyrptonyte lock + pump) I'm overly happy ...

Now the problem is ... I've been using it for a while and I've decided I want to put some slicker tyres on it for a more road set up and use it as a commuter to central London everyday . The tricross is starting to go a bit and I want to make the use of the hellcat so as to not waste money

Iv been asking everywhere and no1 is helping one bit

So this is the problem ....

The rim width is 30mm and at the moment I'm running kenda slant 6 huge bloody things

I want to put some 700 x 35 on there but unsure wether they will be OK as it would be only 5mm more than the rim

So
question 1 : what width can I safely use (35c?)
Question 2 : I'm a big guy so will it be OK
Question 3 : recommendations for tyres

Thanks

Conor