Evicting after taking over tenancy - via Auction

Rent Arrears

Hi All,
First message to the forum, apologies If I make a mistake.
We have just completed on a property through Auction with a tenant in situ.
Last day before completing we came to know about arrears because seller charged us for past four months and they were able to due to hidden conditions in auction made us liable for it.
Facts:

1. Arrears of 4 months or more.
2. I have copy of AST which was not signed by current seller, but an owner from whom current seller bought.
3. No deposit was taken.
4. No previous Gas cert or EICR is available. I am getting new ones done.
5. I have issued section 3 & Section 48 with How to rent guide, EPC and Copy of old AST

My questions

1. Can I issue section 8 given arrears are for more than 4 months. Or I will have to wait for two rents to become over due?
2. Even if I have to wait, does it make sense to hire an eviction specialist to start putting things in place for impending section 8 for arrears in a months time.

Please advise.
Kind Regards
Swati