How Much For A Set Of Clients

I will soon be meeting a few people who plan on selling their clients to me that are currently hosting with them.

I have never bought/sold clients before and would like some guidance from the community here on WHT.

Correct me if im wrong.

I should consider purchasing those clients who's contracts are going to expire soon, preferably within the next 6 months atleast?

Should i or should i not purchase clients who they have recently taken a renewal fee from that will last for atleast another 6 months?

How will calculate on what prices they should be selling their clients to me for? Are they going to add up a years worth of hosting before they set a final sale price?
At the end of the day i dont want to take on clients who have already paid for their hosting and wont be expiring anytime soon. I think, if i take them on board now they will be using up my hosting resources at my expense which i will have to wait until their next renewal is due.

The guys i will be buying the clients from have their current hosting plans as follows:

Monthly prices range from £1.90 £5.00 £9.50 £15.50,

Yearly prices range from £19.00 £50.00 £95.00 £155.00

Depending on what packages their clients are on now, how much do you think on average 5 clients would be worth roughly?

Before i purchase what else do i need to look into?

What other questions do i need to ask other than the likelihood of how long they expect their clients to stay with them/(me).