Of course you need HoT for LS3 and PoF for LS4 besides the unlock I believe. Both are worth making sure you have when you get the expansions not only to the stuff Yobam mentioned, but the access to more ways to get mastery points and other fun stuff to help grow the character. At least, get the LS3 for sure. I only got LS2 parts I missed when it happened to be 50% off for the full bundle, which made the entire thing cheaper than the cost for the parts I did miss. Always buy the bundles when you have the option because it saves you money in the long run. Even the more uber HoT with PoF and gems stuff might not be cheap one shot for some budgets, but best if you really want it because separate they will cost a lot more.
On that note, make sure you ask questions as needed in guild chat and even hop on voice to hang with the crew. We'll make sure you get it figured out and help you see how far you really want to take it ;)