You shouldn't have issues with the characters you listed. Marty is easy enough to use, Rifis shouldn't take effort, and Dean is great, but be ready for Seluf to not be able to fight ever. And yeah, Xavier will be a pain to recruit. Salem can work in combat as long as you don't try to make him specifically a dark magic user, since the only dark magic he's likely to use is rare and heavy. He can use elemental magic just fine, though.
That's all fine by me, gonan wait for more advice about Marty (no offence, he's just been the subject of a lot of controversy), glad to hear about Lifis, suspected that about Dean, fine with Sleuf not fighting, was actually thinking about Dark for Salem so he could eventually fling Fenrirs at people but recognised the Wieght thing and was willing to put Anima on him anyway.
For Manster, you need to have Leaf and Rifis bring any items with them at the end of Ch3 that you'll want for the next few chapters. Make sure you bring the Flame Sword, Light Sword, Lockpick, Armorslayer, and Hero Axe. (You get the Armorslayer in one of the chests in Ch3; the Hero Axe along with the first Pugi are items Othin and Halvan can get from houses in the first chapter. Don't miss them.) Other items aren't as pressing, but bring what you want; just make sure not to bring more than 12 items total. And empty Eyvel's inventory.
All sounds cool to me.
Enemies never drop items in FE5, but it's usually not too difficult to capture enemies with items you want. You can have your axe users practice against enemies in the first few chapters; you won't get anything too great, but it'll help you get the feel of it for later.
Damn! Well, okay then... I knew I was going to have to Capture anyway.
I recommend checking the Gaiden requirements and going for them, also. 2x and 4x in particular let you get important characters and items.
I certainly will do, not sure about 24x though, can I have Sara and Kia without going to it?
Don't shirk from using Dagda. He's amazing as a capture-bot and extra stuff is handy all the time.
He's also a Jeigan... More Capturing is tempting though, can't other people do that too?
Amalda is fucking amazing there is absolutely no reason not to use her. Seriously.
She's the Jugdral equivilant of a Valkyrie and she isn't Mist or Nanna, that's actually a very big reason for me.

The B route (with shanam/miranda) is an absolute motherfucker by the accounts I've heard compared to the A route. Stay away. Plus, the A route get you Sleuf (sexy) and Misha (sexier) so why not?
That's what I thought, thank you.
but a serious tl;dr to mine and othin's posts: if I told Harpoon to just chill the fuck out and roll with it as it goes, I'll right well tell you the same.
chill the fuck out and just roll with it as it goes mang
No thank you, I actually really don't like it when people say this, I'm not equipped to chill out or roll with it, really...