"I've also looked at the diy rear wheel conversions (think a front wheel conversion will kill bike balance, might be wrong) "
I did my front wheel conversion of a Trek 7.2 Fx hybrid for £450. My neighbour did a Cyclotricity (Glenrothes) conversion of front wheel suspension MTB.
Both actually enhance the balance of the bike, with bottle cage batteries.
Definitely a lot better than the Decathlon bike I rode in France with a rear hub and a rear rack battery, that 24kg was totally unbalanced (even though for £500 complete bike I'd still get one!)
Home brew stuff can't be diagnosed easily and spares could be a problem.
And both have had parts swapped in & out (flood, not reliability issue) without much hassle.
Mine has had a lot of use for 5 years with my son sharing it, 10 mile each-way commutes or 3 mile climbs up out of Comely Bank.