WIP_Scale and Biome Help

Disclaimer: WIP RPG Setting - Alpha

Specs: 40x40 Fantasy World - Subtropical Archipelago

Scale: 1 Square = 30 sq miles

I like what I've built thus far, but looking for some constructive criticism and tips to help me move this map forward.

What I'm wondering is this...

\- Are my stamps the right size for my scale? What size brush should I use to cut out my rivers?

\- Thoughts on the southern central island mountain range I created. I like it, but I'm wondering if I've over done it. As for rivers, I plan on adding about 3 to 5 larger ones flowing from that range. The rivers will be accented by cliffs to match their shape. Some will end in lakes, others will end at the sea. Flora to follow that...

\- This archipelago has a subtropical climate similar to our Mediterranean region. What type of individual biomes could be found? How would my mountains, hills, and elevation influence my biomes? Would that small chain of volcanic islands to the northeast effect things? Any desert regions?

I think if I can get a better idea on where my biomes will be, it help me come up with a plan of sorts.

Thanks in advance for any help!