advance rent- are there any implications

Tenancy Types and Management

I am a new landlord, I have found some potential clients who origanally wanted a 12 month tenancy however following there credit check I would want to do a 6 month, which they have said would be fine.

Origanally on the 12 month contract they was going to pay 2 months rent for the first 6 months then the whole year would be paid for.

Now on the 6 month contract they have said they can pay 3 months upfront in dec and then 2 months in Jan, I have already received 1 months deposit and 1 months rent.

Are there any implication to the tenancy if we agreed to this?
if we had to evict them say, does the normal notice still stand?

any help would be appreciated...the tenants are self employed and have said they would like to pay in advance because there business is doing well, and they dont know how it would be in 12 months time.