I thought this first episode of BackAndFork was so much fun! I think the group has a really good mix of experienced and new players when it comes to TTRPG but theyre all doing a great job pushing into that RP world (unsurprising knowing their minecraft rp experience of course)
Since Martyn asked specifically for feedback I would like to mention a few things I picked up on myself (my credentials are: I've been playing dnd for at least 15 years and actively GMing and playing multiple campaigns and oneshots currently, though I have no experience with Daggerheart yet)
1. While difficult to balance and understandable from a content point of view, a few times it felt like martyn rushed the party forward to the next scene a bit too quickly without letting the characters play it out a bit more. An example was Cherri when they pointed out how she wanted to confront the party earlier but martyn had already gone ahead and described how they arrived in Hush.
2. This one I feel like is a bit of a ttrpg faux-pas but it can be done: I would suggest less talking for the players as their characters. a few times (once again I assume in the spirit of keeping the session within an allotted time frame) Martyn would say something in character for a player, and it felt like it was mostly Ren? (if this was something that was pre-discussed because ren or the players in general were a bit shy or worried about their RP obviously that's no issue and in fact a great solution) This can often end up taking some agency away from the players, even if it is most likely what they were gonna do. I would suggest going more along the route of describing the character's feelings or suspicions rather than voicing things for them, as it leaves room for them to add their own spin to what they say and do.
3. More of a tip than specific feedback but I think generally timing wise this ended up going quite well within an expected timeframe, but if you're doing more of a longer form campaign after this, it can be a bit easier to let go of the time pressure to finish the entire thing, I would just plan about 3 or 4 encounters (combat and non-combat included) ahead of where they currently are.
Other than that I would suggest not worrying about pre-writing specific descriptions of everything as that may just take up a lot of time which you can easily fill with your own improv and writing experience (of which Martyn has plenty)
Martyn also mentioned having to make his own maps in the future; I would suggest having a look at existing map libraries out there, there's a bunch of free ones or even cheap paid for ones. I personally am a huge fan of 2-minute tabletop, they do a massive range of pay-what-you-want maps with a lot of variants for the specific maps as well often. I also hear good things about Czepeku but I haven't personally used them yet.
All in all I think Martyn did an absolutely crack up job for his third time ever playing a ttrpg and first time ever GMing one, I know he has a good support group in this party as well with a lot of experience from owen and graecie at least it seems as well.
I hope I didn't come off as rude in this, I just really love the hobby and have been doing it a long time so I can yap forever about it.