I thought Filipino UK was your second home!!
Teasing aside, this is something that I've been researching for several months as I'm just months away from paying off the mortgage. What I'm aiming to do is re-mortgage to release equity in my home to enable me to cash-buy a second property to rent out. Then mortgage property 2 to purchase property 3 and so on.
The buy-to-let sector is buoyant due to the difficulty for first-time-buyers to get a mortgage. At the same time the rates for BTL mortgages are relatively low due to the low BoE base rate. They are higher than non BTL mortgages though.
With regards to Letting Agents, if you're planning to rent out to facilitate a move to the Phils then a LA will be essential. If you're staying local, are quite handy with DIY, know a variety of tradespeople who you can rely on to respond to call-outs 24/7 then you can probably manage without one - although you should probably still use one to find tenants as there is legislation regarding deposits etc that you would need to be aware of.
LA's do a variety of packages from finding and vetting potential tenants to a fully managed service. Charges for a fully managed service range from about 7% up to 15% but it's a competitive market and everyone negotiates. Tenant finder/vetting charges are around a couple of hundred pounds.
For a first time landlord I'd recommend you put everything through a LA until you have the experience to go it alone.
For a better return on investment try student lets (very strong market for that in Derby) but be prepared to re-decorate every year. Be aware of HMO's (houses of multiple occupancy) though as you may need to get an inspection from the local council and pay for a license. Again LA's and estate agents can advise on that.
If you do student lets you will be expected to furnish the property.
Rule of thumb is to work on getting rental income for 10 months a year.
Income from rent is subject to income tax and the lenders and HMRC talk regularly so high risk to try to avoid declaring it.
Mortgage interest, mortgage arrangement fees, LA costs, repairs, re-decorating, EOT cleans etc can be offset against tax but capital improvements (new kitchen, bathroom etc) cannot.
I've heard several nightmare stories and several success stories with buy-to-lets, as with anything there's an element of risk but generally most people seem to make good money at it.
Most landlords aim to achieve approx 7% return which is far better than sticking your money in a bank account. Also over time property values should go up so you will gain twice over.
There's a lot more to it than above, and perhaps you should try to get advice from sources outside this forum, but that should give you a decent start point.
In the meantime try checking property websites such as Rightmove to get a feel for property values and rental incomes.