4 weeks in Malaysia: From KL to "all" Borneo. Lookin for tips!

Hi everyone! I’m an Italian solo traveler planning a 4-week trip to Malaysia this August. I’ve mapped out a day-by-day plan and would love to hear from fellow travelers who have been there: Are there hidden gems I’m missing? Any logistical "traps"?

Phase 1: KL & Melaka

• Aug 7-8: Kuala Lumpur. Focus on Chinatown, Central Market, Sri Mahamariamman, and Thean Hou Temple.
• Aug 9: Day trip to Melaka. Is a day trip enough or do you suggest staying one night to catch the evening vibe?
• Aug 10: Batu Caves (early morning on Monday to avoid the weekend rush) + Merdeka Square and KLCC Park.

Phase 2: Sabah

• Aug 11-12: Flight to Sandakan. Sepilok Orangutan Centre, Rainforest Discovery Centre (RDC), and Labuk Bay.
• Aug 13: Turtle Island (Selingan).
• Aug 14-16: Kinabatangan River. I'm staying with Uncle Tan for a raw, "wild" experience.
• Aug 17-19: Flight to Semporna. 2 full days of snorkeling/diving in the Mabul/Sipadan area.
• Question: For Semporna, I’m looking for the best visual impact—any specific island or spot that is less crowded but visually stunning? I arrive on the 17th and was thinking of searching for snorkeling trips once I'm there. Is that okay, or is it better to book everything in advance?

Phase 3: Sarawak

• Aug 20: Flight to Kuching.
• Aug 21-23: I was planning a tour to Batang Ai for a more immersive experience, but as a solo traveler, the price from Borneo Adventure is quite high. Any suggestions for an authentic alternative to experience longhouse culture?
• Aug 24-25: Bako National Park (overnight stay is a must).
• Aug 26: Free time in Kuching to chill and explore.
• Aug 27: Flight to Mulu (arriving at 12:00). I’m looking to book trekking for the following days. Can I book these on arrival or do they sell out fast in August?
• Aug 28-29: Trekking to Deer & Lang, Clearwater & Wind caves.
• Aug 30: Return to Miri, then back to KL.

Phase 4: Merdeka Day

• Aug 31: Back in KL for Merdeka Day (Independence Day).
• The Dilemma: I was considering a quick run to Cameron Highlands, but I’m worried it might be too touristy or rushed. Should I just stay in KL to witness the Merdeka celebrations instead?

Specific Questions:

1. Merdeka Day: How is the atmosphere in KL on Aug 31st? Any specific spot to experience the parade without being totally crushed by the crowd?
2. Food: I want the real deal. In Kuching and Sandakan, what are the 2 dishes I absolutely cannot miss?
3. Logistics: Are there any specific transport apps (besides Grab) or local tips for moving between these remote areas in Borneo?

I’ve done my homework on costs and logistics, but I value the "boots on the ground" experience of this community. Thank you in advance for any help! 🇲🇾🇮🇹