I've been permanently living in Thailand just before the Covid lockdown, so I'll share my growing tricks.
First, I recommend buying the "van egmond potting soil" at HomePro. My reason for this is that the soil you buy from the local Thai garden centers are full of wood chips, disease, and fungi. Then a couple bags of peat moss / coconut husk chips. I've noticed the Thai brands do just fine. These will serve as barriers to mold and weed invasions.
Secondly, I recommend selecting cherry hybrids adopted for the extreme heat. Example: "Cherry Tomato Sweet Girl" that is sold at HomePro has a 90% seed to germination rate. I find this closely accurate to my 85% rate. (The seeds germinate, but don't penetrate the top soil level, I deem a loss). I've been successful with western seeds, but you will have "end rot" from the heat.
Third, I recommend watering with filtered water. The water here just east of bangkok isn't... let's just say safe. I've noticed in a soil test my soil ph went from a healthy 6.5 to a 7.4 in one growing season using "tap" garden hose water. You should be able to keep the soil that you purchase from HomePro at a good level for 5 years or so.
Finally, I recommend large growing pots or above the ground seed beds after you successfully germinate seeds in growing trays. If you opt for not using growing trays, I see Homepro now sales decomposing grow pots. The reason for starting in these grow pots is because you will need to retransplant the germinates seedlings at 4 weeks to their own pots. This seems to be the "sweet spot" for me with successful seed to plant growth..
***I've always started seedlings in August and transplanted in September with great success. Then I have 4-5 months of good pollination and produce.