The bike needs fairly robust forks.
Probably different front wheel kits are fairly similar to fit. Some (eg Swytch) have a fairly small battery that sits on the handlebars. They are probably a bit easier to fit but have limited range and the weight could affect steering.
Fit a legal 250w kit, and whatever you do don't fit one of the high powered direct drive kits (often advertised as 1000w or 750w). They need high power expensive batteries, are very heavy and have short range. Bad on the rear, probably especially unsuitable on the front wheel.
You might look at one ready built if you don't already have the bike: eg
https://wooshbikes.co.uk/?crusa at £850. That is all reasonable quality components, good quality motor and a battery with a decent size/spec. Battery is significant part of the cost of an ebike. If you are looking to build yourself you might save a bit but make sure you get a suitable battery. (Ask here for more advice; I can't advise too much on many battery details; but they are important.)