As the OP selling his lens, customs and handling charges shouldn't trouble him apart from completing a declaration form.

Have you looked into the pros and cons of using teleconverters to see if one would be suitable for your needs?
https://petapixel.com/2017/04/04/pros-cons-using-teleconverters/

The one you mention isn't too bad but not as good as Pentax's own
HD Pentax-DA 1.4x AW AF Rear Converter
Might be cheaper though!

A novel solution would be the Pentax K mount ZOOM 400-600mm F8-12 Reflex
Pretty scarce, but they do turn up.

https://www.pentaxforums.com/lensreviews/SMC-Pentax-K-400-600mm-F8-12-Reflex-Zoo...

There as one presently listed on eBay (London seller.)

Then there's the newer PLM version too to add to the mix.

Heck no! Why not just use the phone to take the photo? In any event that does sound difficult to do if you don't carry a compatible mobile.
There are other ways that can time sync location data from a dedicated GPS too but surely it is simpler to have the GPS built in, and don't forget the Pentax GPS's so far allow astrotracing ? So I can't agree there is no need for the inbuilt GPS.

Of course they can lock onto items! If yours isn't doing that perhaps it's faulty? Inability to detect eye movement surely has to be the case for all DSLRs unless they have a hybrid system.. Ground glass screens aren't able to identify what's focussed on them, let alone detect eye movement. Other cameras have been designed to do that, or even DSLRs in live view mode, but then they're not being used as a DSLR. So at the end of the day you need the right camera for the task in hand. Any Jack of all trades camera would be a compromise.

The MX-1 shared much of its technology with the Olympus XZ-2 including the sensor and lens. MX-1 development seems to have been dropped when Ricoh took Pentax over soon after the MX-1's release in 2013. There was no successor to the Olympus either so presumably the collaboration ceased.

One does have to be careful posting on sites such as Instagram. They claim it does not take ownership of its users’ content. However their terms state that the user grants them a “non-exclusive, fully paid and royalty-free, transferable, sub-licensable, worldwide license to use their content”.

What this means is that Instagram has all the rights of the original owner of the content – aside from the fact that it is not an exclusive licence. Should a photographer sell an image under an exclusive licence, posting that image on their Instagram would breach that licence.

Hi and welcome to the forum; and well said.

My mention of a NAS seems to haver triggered some curiosity . As folk have said, a NAS is Network Attached Storage. Many are quite capable of hosting a photo gallery and much more.
Here is a link to my site on the NAS: https://jkpg.myqnapcloud.com:8081/piwigo/

It can host galleries, forums, blogs, family history, local storage, anything really!
This YouTube video describes the NAS I presently use.
https://www.youtube.com/watch?v=m4HtC8S7vaM&app=desktop
QNAP make a range of them and there others by Synology. It is even possible to configure a PC to act as a NAS.

The gallery software I happen to use is open source (and free to download and use) from here:
https://piwigo.org/
Piwigo have a demonstration on their site so you can have a play with the backend side of things which is here: https://www.opensourcecms.com/piwigo/

The QNAP does come with its own gallery software which might be easier to use so ultimately what you do use is down to personal preference.

One thing using the DIY hosting method is to consider it is up to you to make any backups even though the data can be duplicated across the drives in the NAS depending on how it has been configured.

However you are not at the whims and fancies of hosting companies who can charge what they like, close down with little or no notice, or drop your gallery or images because they simply don't like them.

It may seem a surprise in that search engine needn't ignore you NAS. I often find when I'm searching for something that the top entry is a link back to my site which maybe why one of my database sites is heading for half a million page views this year.