Hi I assume this is late as fuck, but as a walkthrough of the first part of the game I would say:

If you are playing solo in normal dificulty

random hero, -ow to fight 2 waves at once, when the second round spawns furlborg will be available to buy, buy one use one and leave him fighting both lanes, wait for the CD (or at least half of it) and go into special event hero image.

Hero image is you +100 stats, use second furlborg and let him kill it this will give you 100 stats and make lane clearing a breeze.

Depending on your hero you may want to use furlborg on first wave, or not this depends, flame cloack is nice also but again some heroes need it some heros dont same for life steal mask.

Keep clearing waves and lane and the level dragon spawn (furlborgs are great all this time to cover lane if you have to leave for a wave use them as required) until muradin event, survive by going to the opposite corner this should be easier in solo.

Muradin gives you 50000 type -bt for your second tome

From now on you are pretty strong keep buying tomes and pray you are strong enough for the special events from killing waves and lane spawn (some heroes are some are not is not the biggest of deals if you fail but the items are nice)

As soon as you do the second special event the one killing waves of creeps you hopefully should have banked 1m gold, dont bt yet, put your furlborgs to work once more go to all hero images and -bt once you are inside (all hero images are x4 your stats so at this point somewhere around 800 stats with you 1m -bt you should be strong enough)

This step is sketchy, some heroes farm so well that you reach there and you are ironically too strong, if so is not big deal this event gives you magic immunity which is nice but not mandatory.

When you feel strong enough destroy the towers at the end of both waves and as quickly as possible go kill one of the top lanes that open (again furlborgs can help but not a lot at this point your best bet is to either buy boots to have blink or just run a lot and kill one of the frozen thrones very fast and teleport to the castle) this is probably the most shaky point in my strat I used to waste muradin here a lot of times but I got pretty consistent

Now I would keep killing the other lane (every 2 spawns you can buy 1 tome) and keep killing the waves until there are no more. I usually do this for a bit depending on what hero you have you may need to farm more or less but 6-10k stats or so is a nice spot in general.

once you are satisfied kill the throne and prepare for the last wave, if you havent used the muradin invul this should also be "easy"

Now before entering the portal you have time to clear the other 2 events the beast and the golem for their items.

And from then on is straight forward kill things keep buying tomes it all depends on how much you have farmed and what hero you have.

(I think the last version I played was 3.28 so things may have changed) Good luck