[landlord-US-Connecticut] Screening tenants/vetting, app fees, use Baselane or?…

I had a 2 family 20 years ago, lost it in the 2008 housing crash partly due to me being young and not being good at filtering good/bad tenants.

We just bought a house with an ADU and tenant pre-installed. She pays but constantly brings over sketchy people at all hours of the day and night and smokes, we plan to evict in June when the lease is up.

We use Baselane for rent collection which I believe has a tenant screening / application system. Has anyone used it? Is it good? What about Zillow or others?

What fee do you charge for applications? I can’t tell if Baselane charges the fee directly to the applicant or if they charge me and if so how I roll that into the application fee.

Guidance needed here, treat me like a child. Hold my hand please.