Strong "A Wand for Skitter" vibes from this post.
I don't get the refererence, probably a fanfic, no?
I have a couple spells I'd like to get. From our currently unlocked spells I feel like the enlargement/reduction spells along with waddiwasi is absolutely vital, it's exceptionally potent for just being able to launch large objects, and that's not even getting into the things the individual spells can do, like shrinking an opponent's hand so they can't hold their wand for example.
Getting the vanishing spell would probably be a good bonus to our defence. Grabbing a deep understanding of spongify would be great as well.
I'd also like something that acts as the equivalent of protego but for our offense. I'm not 100% sure what exactly would do that, maybe one of the blasting curses? Dark magic could also be a good one for that type of stuff.
Otherwise getting something with the "maxima" tag would be awesome since that can apply to who whole bunch of other spells, bombarda maxima might be a good one so that we get a blasting spell and the maxima thing at once. We know lumos maxima exists and it would likely get bright enough to actually blind enemies, protego maxima also exists (though it's not very useful for our purposes). Jacob is very good at finding patterns in magic and I would like to see what he could do with the maxima addition.
Yeah, Waddiwasi with Engorgio seems like a great combo, especially to deal with creatures resistant to magic... I would also like to get the Deep Understanding of every spell available since they add a lot of extra firepowers and versatility.
About the Maxima command, I don´t think that we will be able to learn it and apply it directly our spells, most likely it will be another level like Deep Understanding.
I'd also like to try and immitate Basques a little more in two specific ways.
The first being her physical enhancements via magic. Many wizards don't seem to have that type of ability and it would be a huge leg up. It'd also help against many other magical dangers we'd be going up against. Also being able to wiggle a wand more quickly allows for spells to be shot off much more quickly
The second is I'd like to actually bond with some type of creature like she did, ideally something with some very interesting magical abilities so we can get insights like our dear ancestor did. Nelly is one that comes to mind, trying to replicate house elf magic would be very useful, they are amazing at wandless magic and have a grasp over lots of seemingly simple charms that would be an amazing addition to Jacob's abilites.
A pheonix would also be nice, both for not having to worry about them and for their insights into fire magic. Bonding to an obscural would be something interesting as well. A Thunderbird would be cool. Maybe we could swing a basalisk and pick up parseltounge along the way. Or go the Lobo route and bond to a mundane animal that's aware of magic, a wolf or big cat would be a cool one. Some type of bird like a raven would also be pretty neat.
About the first part, there are several potions and remains of magical creatures that significantly enhance several aspects of the user, but they only work for a limited time ad it seems to have really bad side effects if abused.
As for the second part... I totally disagree with magically bonding with Nelly, she, like all the House Elfs, is a sapient being and treating her like she was an interesting pet is pretty disgusting (and exactly the same happens with an obscurial)
And you really need to temper your expectations, Fenixes, Thunderbirds, and Basilisks are not only extremely rare (and in the basilisk's case extremely dangerous), but also extremely difficult to treat without being an absolute expert on the field of magical creatures... The magical creature we are most likely to bond with since we would be able to buy, take care of it, and it is accepted as a pet would be something like a kneazle.
We will be able to interact and tame/befriend several magical creatures in Hogwarts, but I really doubt that we can take them home with us.
Maybe we could make stuff and sell it to the ministry like Fred and George did in canon, whether we sell the patent or actually manufacture the stuff is something to debate. We might even be able to swing a time turner that way "I need the extra time to fufil your orders I swear Mr Government".
As for what we make, we could rip off the protego hats from canon (make it into a belt instead maybe? Harder to remove that way) or make our own things. Maybe a wristband that allows the user to use a wandless accio to summon back their wand once disarmed? Our boots or goggles would also be very potent tools in the hands of aurors, so we already have something we can make there.
The problem with selling alchemical items is that they require a lot of actions to create, we would need at least 2 Personal actions for each item... Potions are much more time efficient, we can make batches of up to 5 with a single regular action.