If you rent it out the chances are you’d need to switch to a buy to let mortgage (I don’t know if banks are happy to do consent to let these days). The interest rate may be higher, you may have an early repayment charge in your current mortgage.
Are you a 20% or 40% tax payer (after the rent less rental expenses is added on to your income!). Assuming £250 a month costs, your net rental income is £1,000 a month. If £12k Pa pushes you into 40% tax zone, that’s £480 a month tax, before reducing it for 20% of the mortgage interest (not the repayment part, just the interest). You’re likely at a loss at this point.
If you’re paying rent to live elsewhere that’s likely more than your current mortgage. On top of the loss you’re making on your rental. Or if you buy elsewhere you have to share the equity between the two homes (two big mortgages, both at higher interest rates as loan to value is worse). Plus you’d need to pay higher stamp duty on your new house ( if in England, not sure about the others) as you’re not selling your existing home - add 5% in top of the normal stamp duty.
If you don’t know how to comply with the legislation you need a managing agent (always been great in my experience).
Wear and tear is generally far greater in a rental. Be prepared for decorating every 5 years or so, carpets more regularly than you would, etc.
Be prepared to be left a filthy flea-infested home even from an apparently decent tenant (true story). I wouldn’t rent out something I had an emotional attachment to ever again.
I’m sure you can make your dream work, but you might need to get there through a slightly longer term plan? I agree with you that it would be foolish to get off the housing ladder.