I live and work in Kendal which I think ticks a lot of your boxes.
It's not quite a York, Canterbury or Bath, but it is an interesting town with plenty of history and some unique features, as well as its own castle (in ruins, admittedly, and possibly not the most photogenic).
It's midway between the Dales and the Lakes so ideal in that respect.
There are plenty of sleepy hamlets. Sorry, I don't know Clovelly, but there are some great little spots here and there. Personally, I love Troutbeck and the Troutbeck valley, as well as Kentmere, which are both only a short drive away.
Windermere is only a 15-20 minute drive away.
Beaches... there are one or two within relatively easy reach. Morecambe Bay of course is close by too. You can get some beautiful sunsets over the bay.
I don't know Sissinghurst Castle Garden. A short drive from here we have Sizergh Castle & Gardens and fractionally further afield there's Holker Hall & Gardens (where this is also an annual garden festival).
I hope all this is of interest. If it does sound like the place for you, by all means drop me an email (I'm assuming you have access to my email address through this forum) with any questions. We have a lovely holiday let here but I'll refrain from posting a web address. I read the forum rules and saw that you couldn't link to shops in your signature, but wasn't sure about something like this... I'll err on the side of caution, therefore, and not post it. In any case, I'm sure you could work it out if you wanted to.