Landside, most of continental SEA July should be rainy, however depending on the places it's not as bad as it sounds
I've already traveled northern Thailand (Chiang Mai and the hills area) was rainy but OK, Laos is very close to Thailand, Luang Prabang is a great little city with dozens of templs/monasteries it usually rains from 2PM to 5PM and anyway it's too hot outside to walk., Cambodia Siem Reap is OK, the monsoon doesn't feel as wet as the neighboring countries.
I wouldn't trip Vietnam for a few days though, it can be be very rainy and with 4 days you'd be able to travel the South part (Mekong delta) which would be very rainy it's a pity because you're on a boat on the Mekong most of the time.
If you go on the southern peninsular SEA, eastern coast of Malaysia is dry, Perhentian island are beautiful and quite cheap, however it's a crowded backpacker place. The diving is OK.
That leads us to diving now. Borneo is fine weatherwise, Sipadan is one of the best place for fish school action but it can be expensive. Borneo is also a place for jungle walks and nature treks.
A part of Indonesia is quite dry, unlike what I've read above I would say there is only a part of indonesia that is dry and not too windy at that time, it's the Nusa Tenggara area from Bali to Timor, you can also add some places like Pulau Weh and a part of North Sulawesi.
Weh is very cheap but the diving doesn't rate as high as Bali, Komodo or Alor for instance. If you like nature, crossing the big island of Flores is really worth, it's a beautiful island with spectaculat nature and highlights (Mount Kelimutu colored lakes). You can start the journey from Labuan bajo which is also the departing point to Komodo.
As for the Phils, the diving is good and can be cheap but I would advise staying in the southern Visayas (Cebu) where you can dive almost 365 days on some spots esp Moalboal for sardine schools and Pescador colorful walls, If you go to Malapascua or Bohol, be careful to be flexible for your return dates, you may be stranded on the island for a few days with no ferries to go back to Cebu (happened t o me a few times).
I would forget Maldives in your trip, more expensive than the rest of Asia, and a bit out of your way.