What net profit are you expecting, really? You are barely covering the mortgage interest after applying tax and the tax credit.

I would sell.

On these numbers you have no choice but to go Openrent. Plus if you are organised and prepared to put some effort in to remaining on top of legislation and prepared to undertake viewings yourself then it’s pretty easy to be fair.

Any additional income you make will be taxed at 40%. It’s almost impossible to make BTL work for higher rate taxpayers nowadays. If you use a company or are a basic rate taxpayer there is more of a chance but even then the numbers are pretty grim.

Personally I self-manage because I don’t really trust agents, they look to screw you as much as they can and I like to know my tenants and keep an eye on my property. And it’s cheaper.

Your ideal. Every buy to let portfolio is backed by a good career salary. All the other numbers don’t matter.

I don't think the first two options are financially viable.

There's another option where you use an online agent for help with tenant finding. I think openrent offer accompanied viewings amd other extras like that. 

There are loads of BTL calculators online. There's even a gov.uk one. I recommend you use any of them.

Educate yourself on the compliance rules. If you live near the property and are willing to put in some work (if you know what you’re doing it’s not too much. Services like safe2 and hello neighbour (better than openrent IMO) are my go to. Combine with rent guarantee insurance. Most importantly if you do decide to self manage don’t skimp to tough referencing - some questionable tenants find going direct to amateur landlords the easiest way to sneak through their disastrous credit history and proceed to not pay anything!

Also your almost certainly better to run it though a Ltd company. If your not confident with this consider something like getground or provestor

My experience is fully managed has been a nightmare and it's far less hassle to self manage. So option where agent just finds a tenant at 90% of one months rent would be attractive to me.

Other costs not taken into account is insurance, service of boiler and GSC and costs of maintenance such as gardening or repairs.

Future potential costs could be new EPC rules and upgrades to property if not already 'C' or above. Future renovation costs like a new bathroom or kitchen / boiler.

Redecoration costs after tenancies.

Have you approached your mortgage company for permission to change mortgage to BTL and is the interest rate for that known?

I do get why you want to keep your property as a backup home and your realistic that its not going to make you much if any money which is good. Best of luck.

You'll need to get a new mortgage if the current one is for you as the owner-occupier. It will be more expensive.

Any capital gains you might make on a final sale will be subject to CGT, reduced in proportion of time you lived in it as your principal residence.

Only a fraction of your financing costs will be allowable as an expense when computing your net income for tax purposes. You can get around this by setting up a limited company, and selling the property to it, but then you'll have a lot of other costs.

Also, if you buy another house to live in, you'll be subject to a lot more SDLT on the purchase.

Basically, the government is giving you a massive incentive to sell.