Are Balsam Hill trees really worth it?
Is pre-lit a true game-changer?
6ft or 7ft for a standard size house?
What’s the best tree “type” – fir, spruce, etc?
It depends on what you're looking for... I find BH trees too dense for my liking, I want to get lights and decorations right in, like two per branch minimum but preferably more and down to the trunk. It doesn't look like you can achieve that much from Balsam Hill trees because there's so many branches. They're also unnaturally regular looking, although I'd assume you might be able to arrange the branches to look a little irregular if you wanted?
I didn't find pre-lit worked well for me because in the third year, the lights simply stopped working (the second year they flickered a lot which was annoying). So from then on I just put whatever lights I wanted on, which was nicer because some years I wanted colours, some years a nice warm white. It was nice not having to wrestle with getting light strings on and off, so it might be worth it to you (if the lights don't fail, that is!) if that's an aspect you really loathe.
Our tree is 7ft, we put it in the bay window and bend down the branches that are against the low wall of the bay. They don't get seen by anyone so no point putting lights or decorations on them. The tree topper is very close to the ceiling of the bay, so maybe worth finding out how high your ceiling is where you're going to site the tree if it looks lower than average? If ours wasn't tucked in the bay there would be loads of head height.
Tree type depends on what you like. I don't know what ours is supposed to be either, it's frosted with fake snow that falls off every year and is a pig to vacuum up and I still find sequins from it around the skirting boards in July March.
I don't think you can get pre-lit multi-coloured, I haven't seen any. Hopefully if they do exist someone can provide a link. Coloured lights these days tend to be LEDs which aren't quite the same as the filament bulb type, the red tends to dominate rather over the other colours. The sets we had in the 70s were definitely more pastel than modern ones, no idea why but I loved them. Last year I had four shades of "white" on ours, a coppery white, antique gold, champagne gold and cool white which twinkled, I think I'll be putting those back on this year.