The answer to your first question regarding speeding up flowering- You can speed it up with more light and optimum temps. Using an HPS will get you there a couple weeks sooner than CFL's. If you already have an HPS, then adding another won't make as much of a difference. For the most part, it's strain dependent and you can only speed things up by maybe a few days or a week...

The buds will form slowly but surely. They won't fatten up until the last couple weeks though, so just be patient.

Don't give them nutrients high in N anymore, some is OK. Look into Canna nutes, they have a nice website with instructions and dealers all over the UK. You should only need the Terra Flores. The PK 13/14 is optional but recommended. Terra Flores | CANNA UK