Draalo

Autostruts are only availiable if the setting "Advanced Tweakables" is on (and if normal struts have been resarched) Maybe you activated that setting?

Look at your NavBall - its facing up. Should be facing forward Rightclick your probecore and change the direction.

On the bottom left in flight screen there should be a blinking green light. When staging is locked it turns red.

The 2.5m Heatshield provides plenty, dont worry. If your goal is to reduce mass: From Eve coming 75% ablator should be enough, you can even try 50%. (Dont forget to remove monopropellant from the capsule if its your goal )

Yes, it must be two seperate launches. But the docking vessel dont have to be manned. Just build a tiny probe with a HECS, solar and proper antenna with a docking Junior port and park it in Duna orbit. 2 Oscar B tanks + a Spark engine will give you plenty of dV with very low cost. Edit: Once the contract is fullfilled you can undock again, no need to bring the dead mass back to Kerbin. If possible use a proper relay antenna so your leftover will still act as a relay sat for future missions without extra costs

PE has to be outside the atmosphere so at minimum 70km

Are the parts inducing drag mounted to the node inside the cargo bays or attached to the surface inside? As far as i now KSP considers parts mounted to the surface as mounted outside. Test it. mount a small tank inside the bay to the node. attach 8 Batteries radial to that tank. Does it still produce drag?

A Sentinel has to be lower (AP/PE) than the target planet to detect some over time. It covers the space from the planet below PE and the planet above AP @Hotel26: Inclination doesnt matter

Cargo Bays have different buyoncy when open or closed

Well, i took the 4way thrusters for the example pictures - yes, not optimal. But there are monodirectional thrusters too I build leightweight ComSats all the time. HECS probecore, 3x static solar, RA2 antenna, one battery, smallest monoprop tank and a pair of monodirectional thrusters below. Vessel mass below 0.5to., has about 230m/s dV - enough for manouvering around Mun and Minmus. Easy to send 4 of them with one launch.

First go to settings and activate "advanced tweakables". In the VAB you can rightclick the RCS thrusters then and choose "show actuation toogles", should look like: Switch on "Force by Throttle". RCS must be turned on when thrusters shall fire. Hint: if you deactivate yaw, pitch and roll the SAS wont use the thrusters anymore - no waste of monopropellant if vessel is just reorientating but still full RCS capabilities when using IJKL for docking

Those specifics are hidden. If you have to scan for objects endangering Duna AP/PE of Sentinel has to be between Kerbin and Duna.

Build a vessel - any kind, using RCS. Launch. Hit ALT-F12, use cheat menu getting into otbit. Activate RCS, press and hold the H-key. Stop the time until monoprop is done and compare orbital speed at end and beginning. Get an idea

Its a matter of density, not gravity. All which is less dense than the liquid will float regardless of how strong the gravity is

Vessels are not globaly stored. If you want to load from a different save game use: KSP Craft Organizer