Yes, and yes!
> a) can you build a route consisting of several sections, where each section has a different amount of curvature
Do it in stages - which is what you have to do anyway since you're after different curvature for certain sections.
Step 1:
Create each sub-section of your route. Each one can have different curvature.
Use the 'Create Scenic Routes' option at the top level of the web Route Lab (https://www.myrouteapp.com/routelab)
- select 'Create a scenic roundtour' and make it 'Create a scenic route'
- add your start and end points for this sub-section of the route
- pick your wiggle factor (see Lynchy's screenshots above)
- save the route
- repeat for all the different subsection that make up your full route
Step 2:
Stitch together the sub-routes into your full route.
- create a new route
- in the lefthand menu (where it says 'Waypoints') tap the 3-bar menu & pick 'Routes'
- add your (sub-)route
- add another (sub-)route, etc
- for each route you've added, press '+' and decide where to add it ('Beginning' or 'End').
- then convert from route-track to route so you have waypoints you can edit if you want to fine-tune it ('Edit route-track' option -> 'use as route')
Limitations:
- you need to keep below 200 waypoints for the final route, so keep an eye on your sub-route waypoint count.
- you can't juggle the subroute order after merging them with 'Beginning'/'End', so you name your sub-routes carefully to help get the merge order correct
> b) alternative to route-trip generation.... the scenario..... i want to meet someone in a cafe 20 miles away in about 2hrs.
The 'Create Scenic Routes' option at the top level of the web Route Lab will take time as well as distance as the main driver for your scenic route