Having been a gardener for most of my Adult life I have gained a lot of experience, the availability of good compost there to buy in bulk is likely to be sparse, you can get it from Shopee but only small bags around a couple of kilos, they also have seed collections about 20 packets of seed at ridiculously low prices, to store seeds well you need to keep them cool, I used to store my seed in the salad drawer of my fridge in a sealed box.
It is highly possible for you to make you own seed compost, start off with some good black friable loam/soil, riddle this to take out any stones and then heat sterilise it, perhaps by putting it in a metal pail or some form of small metal drum and hang it over an open fire, to this you would add some coarse washed building sand plus rice hulls (do not be too hasty in getting rid of the rice hulls you have already? they add lots of benefits to your garden soil, for a seed compost you will not need to consider to fertilise it what is in the soil you use will supply enough to it.
Two problems you will face growing plants in PH even up in them there mountains and that is; the heat of the midday and late afternoon sun and the predominance there of insects, if it was me I would grow in a form of polytunnel covered in shade netting on the two sides that get the sun, with the rest being covered with a half inch mesh, this would have to be completely enclosed to keep out the Butterflies, that would solve the problem with caterpillars, as for other insects you can make up a semi organic insecticide, using soap, chilli and garlic, the juice from boiled up Tobacco leaves is also a strong deterrent and the leaves are readily available and quite cheap, but do not use this on Tomato plants. Consider using raised beds in the tunnel and save your back.
Growing out in open ground again consider to incorporate both the coarse sand and rice hulls in the top few inches, raised beds there are also good and you could make a type of Cloche frame over the top to provide shading, in a raised bed that is properly prepared you can use intensive culture, where you cut the spacing down between the plants to only half the distance as they get a better chance to deep root.
There is two garden tools not readily available in PH the first and most important is the Dutch Hoe, a draw hoe can be had but they are not near as good, the other thing is a garden fork, you can get something similar but they are more of a hay fork and the tines are just not strong enough.
It seems to me that at present you are in UK where I am also, PM me if you need my phone number and we can talk more on this subject if you wish? also I can advise you what to send over to PH to help with your Gardening Adventure there.