I noticed you did not mention owning any tools.
It is very hard to give advice without seeing the plan.
A fixed table takes up a lot of space and gets boring fast.
I do not think you can put too much terrain on a table but some gamers hate it. It makes the math problem harder.
I like scale stairs. I use adapters for the miniature when it is necessary.
I like Hirst Arts. I build buildings from wood blocks. Carving them from foam is an option if you do not have tools.I did not understand your question about the bridge.
Water is easy but it depends on your base material.
Paint is a totally different issue. Latex house paint and craft paint are best for terrain. House paint is available in sample sizes in any color. Large brushes and sponges are best for terrain.
Textured flock is also important.Do not use sand use saw dust.
The bridge is plywood.The end are separate so I can use it on diffrent tables.
the rocks and bank are pine bark
the texture on the bridge and table is drywall filler/Mud
the water is one coat of Modge Podge over true blue craft paint.
the ground work was painted in several grays and browns befor it was flocked. Add water last.
Dry brush dark to light
The drywall filler almost looks like snow.
I used plywood because this table was going to stay at the store. I use modular terrain at home.
drywall tape
I cut the plywood with a jig saw at an angle to make the bank.
The Plan
From my pre Movie Goblin town.
From Hirst Arts and completely modular.
There are a lots of ways to make rocks. I can make some more useful suggestions with a plan.
Stair adapter